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Plate  I.     Grays  Peak,  Rocky  Mountains  of  C'olorado 


N.\     -. 


ELEMENTARY 


PHYSICAL    GEOGRAPHY 


BY 


WILLIAM  MORRIS   DAVIS 

Stukgis-Hoopkb  Professor  of  Geology  in 
Harvard  University 


GINN  &  COMPANY 

BOSTON  •  NEW  YORK  •  CHICAGO  •  LONDON 


Entered  at  Stationers'  Hall 


Copyright,  1902,  by 
WILLIAM  MORRIS  DAVIS 


ALL  BIGHTS  RESERVEI) 
68.1 


1Ef)t  fltftenatum  Jf^rtH 

GINN  &   COMPANY  •  PRO- 
PRIETORS .  BOSTON  •  U.S.A. 


PREFACE 

The  educational  progress  of  recent  years  has  resulted 
in  two  profitable  advances  for  the  venerable  subject  of 
Geography.  A  strong  feeling  has  been  developed  in  favor 
of  treating  the  subject  as  a  whole  more  rationally  than 
heretofore,  and  a  wholesome  desire  has  arisen  in  favor  of 
introducing  some  of  its  scientific  aspects  more  generally 
into  the  school  course.  A  natural  accompaniment  of  this 
progress  has  been  a  demand  for  text-books  that  shall  present 
Physical  Geography  in  its  modern  scientific  development 
as  well  as  in  an  elementary  form.  The  present  book, 
reduced  from  the  author's  "Physical  Geography,"  has  been 
prepared  to  meet  this  demand. 

The  reduction  of  the  earlier  book  to  the  present  volume 
has  been  made  chiefly  by  omitting  the  more  advanced 
problems  and  by  simplifying  and  abbreviating  the  treat- 
ment of  the  remainder;  but  the  chapter  on  The  Atmos- 
phere is  here  given  a  greater  length  than  before ;  and  a  new 
chapter  is  added  on  The  Distribution  of  Plants,  Animals, 
and  Man,  considered  from  a  physiographic  standpoirit. 
Several  topics  of  a  somewhat  more  advanced  nature  than 
the  rest  of  the  text,  and  yet  of  too  great  importance  to  be 
omitted  altogether,  are  placed  in  supplements  to  Chap- 
ters I,  II,  and  III. 


iv  PREFACE 

The  plan  of  this  volume  is,  like  that  of  its  predecessor, 
to  give  the  problems  of  Physical  Geography  a  rational 
treatment.  The  object  of  this  method  is  not  simply  to 
explain  physiographic  facts,  but  through  explanation  to 
increase  the  appreciation  of  the  facts  themselves.  It  is, 
however,  not  enough  that  physiographic  facts  should  be 
associated  with  their  causes ;  they  must  also  be  seen  in 
relation  to  their  consequences  if  their  full  importance  is 
to  be  realized.  This  relation  must  not  be  presented  merely 
as  an  afterthought,  in  a  detached  chapter  at  the  end  of  a 
book;  it  must  accompany  the  presentation  of  the  facts 
themselves.  As  Guyot  long  ago  said  so  well:  "To 
describe,  without  rising  to  the  causes,  or  descending  to 
the  consequences,  is  no  more  science  than  merely  and 
simply  to  relate  a  fact  of  which  one  has  been  a  witness." 
The  ideas  of  cause  and  of  consequence,  one  preceding, 
the  other  following,  the  physiographic  fact,  have  therefore 
been  held  constantly  in  mind  by  the  author ;  they  should 
be  no  less  constantly  remembered  by  the  teacher  and 
impressed  upon  the  pupil. 

Yet,  while  the  causal  notion  is  introduced  as  far  as 
possible,  it  must  be  recognized  that  certain  facts  of  great 
importance  cannot  be  really  accounted  for  in  an  elementary 
book.  Such  facts  must  therefore  be  described  rather  than 
explained.  For  example,  the  rotation  of  the  earth  and  the 
separation  of  continental  masses  from  ocean  basins  are 
subjects  of  great  importance ;  they  must  be  described,  and 
their  consequences  deserve  careful  attention,  but  their 
causes  involve  speculative  investigation  of  a  grade  that 
far  transcends  the  reach  of  an  elementary  text.     Again, 


PREFACE  V 

the  simpler  phenomena  of  the  tides  must  be  presented  ; 
their  period  may  be  correlated  with  the  movement  of  the 
moon,  and  the  moon  may  be  thus  indicated  as  their  chief 
cause ;  but  the  relation  between  lunar  cause  and  tidal 
effect  cannot  be  demonstrated  to  young  pupils.  A  mere 
outline  of  theory,  with  the  briefest  consideration  of  the 
joint  action  of  sun  and  moon,  is  introduced  in  the  sup- 
plement to  Chapter  III. 

The  general  circulation  of  the  atmosphere  is  also  far 
beyond  elementary  explanation.  The  circulation  may  be 
not  unreasonably  asserted  to  depend  on  the  differences 
between  equatorial  and  polar  temperatures ;  but  the  more 
intelligent  the  pupil,  the  less  can  he  be  satisfied  with 
a  simple  conventional  origin  of  the  prevailing  westerly 
winds.  Explanation  of  this  complicated  problem  is  there- 
fore touched  upon  lightly ;  while  emphasis  is  given  to  the 
elements  of  which  the  circulation  consists,  to  the  correla- 
tion of  these  elements,  and  to  the  deduction  of  climatic 
conditions  from  them.  The  deflective  effect  of  the  earth's 
rotation  is  almost  universally  misunderstood,  because  it 
cannot  be  fully  explained  in  an  elementary  manner.  Its 
quality  is  briefly  asserted  in  the  text,  and  on  account  of 
its  importance  a  correct  explanation  in  the  simplest  pos- 
sible form  is  inserted  in  the  supplement  to  Chapter  II ; 
but  neither  this  supplement  nor  that  on  the  tides  should 
be  studied  by  the  youngest  pupils. 

On  the  other  hand,  the  forms  of  the  lands  have  not  as  a 
rule  been  sufficiently  explained  in  text-books  on  Physical 
Geography.  Fifty  years  ago  there  was  justification  for 
the  empirical  treatment  and  even  for  the  neglect  of  land 


vi  PREFACE 

forms,  in  the  ignorance  of  geographers  concerning  their 
origin ;  but  the  investigations  of  the  last  thirty  years  have 
thrown  a  flood  of  light  on  this  important  division  of  the 
subject,  and  to-day  it  may  be  treated  as  rationally  as  any 
other.  Many  problems,  formerly  obscure,  are  now  seen  to 
be  essentially  simple  and  to  lie  entirely  within  the  reach 
of  elementary  treatment.  It  has  thus  become  possible  to 
extend  the  explanatory  method,  long  familiar  in  the  study 
of  the  atmosphere  and  the  ocean,  to  the  lands  as  well; 
and  to  present  plains  and  plateaus,  mountains  and  volca- 
noes, rivers,  valleys,  and  shore  lines  under  a  rational 
system.  It  is  believed  that  this  division  of  the  subject 
is  here  treated  in  a  manner  more  systematic  and  compre- 
hensive and  at  the  same  time  more  simple  and  reasonable 
than  is  the  case  in  any  other  elementary  book.  It  should 
however  be  carefully  borne  in  mind  that  the  explanation 
of  the  processes  which  are  involved  in  the  dissection  of 
a  plateau,  for  example,  is  not  introduced  merely  that  the 
past  history  of  the  plateau  shall  become  known,  but 
chiefly  that  the  existing  features  and  especially  the 
systematic  correlation  of  these  features  shall  be  better 
perceived  and  remembered. 

While  the  list  of  topics  treated  will,  it  is  believed,  be 
found  exceptionally  full  for  an  elementary  book,  it  has 
nevertheless  been  necessary  to  go  somewhat  against  time- 
honored  traditions  in  omitting  certain  subjects.  Elemen- 
tary text-books  should  not  present  an  encyclopedic  richness 
of  contents,  as  if  to  show  the  learning  of  their  authors ; 
they  should  provide  a  well-selected  body  of  useful  infor- 
mation having  disciplinary  value,  pertinent  to  their  subject 


PREFACE  vii 

and  appropriate  to  young  pupils.  It  has  therefore  been 
decided  to  follow  carefully  the  outline  of  Physical  Geog- 
raphy lately  prepared  for  and  published  by  the  National 
Educational  Association,  and  to  exclude  certain  traditional 
but  irrelevant  topics  belonging  properly  to  Astronomy, 
Geology,  and  Biology.  It  has  also  been  deemed  expedient 
to  omit  certain  other  relatively  advanced  topics ;  such,  for 
example,  as  the  distribution  of  atmospheric  pressure,  shown 
by  charts  of  isobaric  lines,  which  have  been,  it  may  be  said, 
fashionable  since  the  publication  of  Buchan's  excellent 
charts  of  these  elements.  Important  as  are  the  facts  thus 
shown  for  the  more  advanced  study  of  meteorology,  they 
have  no  immediate  climatic  importance,  and  their  proper 
use  involves  so  many  advanced  considerations  that  they  are 
best  excluded  from  elementary  study.  Again,  there  is  a 
chart  of  cotidal  lines,  purporting  to  show  the  advance  of 
the  tidal  wave  through  the  oceans,  which  has  been  repeat- 
edly copied  since  it  was  first  published  by  Whewell  in  1 833  ; 
but  this  pleasing  generalization  is  omitted  here  because  it 
was  discredited  by  its  very  author  in  1835,  and  because 
it  has  never  since  then  received  the  approval  of  experts  in 
tidal  investigation.  The  best  chart  of  cotidal  lines,  that 
of  Berghaus'  Physical  Atlas  (reproduced  in  the  United 
States  Coast  Survey  Report  for  1900,  Appendix  No.  7, 
Figure  25),  leaves  the  open  oceans  blank. 

The  method  of  presentation  adopted  is  sometimes  induc- 
tive, sometimes  deductive,  according  to  the  subject  in  hand. 
The  inductive  method  is  more  largely  used,  because  young 
pupils  are  as  a  rule  better  able  to  learn  from  direct  descrip- 
tion than  from  inferences  based  on  general  principles.    The 


viii  PREFACE 

exercises  suggested  for  the  study  of  weather  maps,  in  the 
supplement  to  Chapter  II,  are  purely  inductive ;  and  the  sev- 
eral chapters  on  the  development  of  land  forms  are  largely 
inductive.  But  it  must  not  be  forgotten  that  the  simpler 
processes  of  deduction  are  perfectly  familiar  to  young 
pupils,  and  may  be  safely  employed  in  teaching  where 
they  are  appropriate  to  the  topic  in  hand.  It  is  indeed 
advisable  that  the  pupil  should  gain  some  experience  in 
deduction  as  well  as  in  induction,  and  Physical  Geography 
should  be  recognized  as  presenting  ample  opportunity 
for  the  exercise  and  development  of  both  these  mental 
processes.  The  relation  of  rainfall  to  the  several  mem- 
bers of  the  atmospheric  circulation  may  be  instanced  as 
appropriately  deductive,  because  of  the  systematic  rela- 
tions of  these  topics. 

The  illustrations  in  the  chapters  on  land  forms  are  of 
two  kinds.  The  block  diagrams  represent  ideal  types. 
The 'views  of  actual  landscapes  in  woodcuts  and  plates 
serve  as  examples  of  the  ideal  types.  The  block  diagrams 
are  in  several  respects  more  comprehensive  than  any 
actual  view  can  be.  They  show  so  large  an  area,  from  so 
elevated  a  point  of  view,  that  the  relation  of  the  parts  to 
the  whole  is  easily  perceived;  they  omit  numerous  and 
frequently  irrelevant  details  by  which  the  pupil's  attention 
might  be  distracted ;  they  present  in  the  most  elementary 
manner  possible  the  correlation  of  underground 'structure 
and  surface  form;  and  in  this  respect  they  are  far  supe- 
rior to  mere  geological  sections,  in  which  the  land  surface 
is  represented  only  by  a  profile  line  which  few  young 
pupils  can  translate  into  a  topographic  form.    Exercises  in 


PREFACE  ix 

drawing  simple  outline  maps  from  the  block  diagrams  are 
frequently  suggested,  in  order  to  insure  the  recognition 
of  the  essential  features  of  the  type.  It  will  also  be  found 
useful  to  ask  the  pupil  to  indicate  the  relation  of  a  view 
to  its  type  diagram,  as  is  done  in  the  text  for  Figures  71 
and  73,  and  for  Figures  141  and  142. 

The  questions  inserted  in  the  text  are  intended  to  aid 
the  pupil  in  learning  his  lessons;  the  questions  at  the  end 
of  the  chapters  are  intended  for  use  by  the  teacher  in  tests 
and  reviews  after  the  lessons  have  been  learned.  If  it  is 
desired  to  extend  the  time  devoted  to  Physical  Geography 
by  classes  whose  average  age  is  somewhat  above  that  for 
which  this  book  may  be  used,  all  of  the  text,  as  well  as  the 
supplements  to  Chapters  I,  II,  and  III,  may  be  studied  in 
full.  If  it  is  desired  to  shorten  the  course,  the  supple- 
ments may  be  passed  over,  the  number  of  map  drawings 
may  be  decreased,  and  certain  sections  that  are  concerned 
with  relatively  advanced  topics  (for  example,  Sections  99, 
103,  107,  124)  may  be  omitted. 

The  teacher  will  find  it  practically  convenient  to  indi- 
cate by  a  brief  reference  in  the  page  margin  the  books  and 
maps  mentioned  in  the  Appendix.  The  examples  there 
referred  to  should  be  supplemented  as  far  as  possible  by 
local  examples  observable  at  or  near  the  school.  Illustra- 
tions of  many  topics  treated  in  Chapter  II  will  be  found 
in  the  ordinary  observation  of  passing  weather  phenomena. 
Many  of  the  activities  of  the  lands  may  be  illustrated  by 
local  excursions,  for  which  the  Efutumn  is  a  convenient 
season;  while  examples  of  the  land  forms  seen  in  the 
school  neighborhood   should   be  studied   in   the   spring. 


X  FREFACE 

Inasmuch  as  land  forms  vary  greatly  from  place  to  place, 
no  general  guide  can  be  of  service  in  this  division  of  the 
subject;  but  teachers  are  advised  to  make  themselves 
familiar  with  their  school  district  by  frequent  excursions, 
and  to  use  as  far  as  possible  all  the  appropriate  illustra- 
tions that  they  discover. 

The  author  desires  to  express  his  thanks  to  a  number  of 
his  correspondents  who  have  supplied  photographs  from 
which  several  of  the  plates  have  been  copied,  and  also  to 
a  number  of  teachers  and  others  who  have  accepted  the 
fatiguing  task  of  criticising  his  manuscripts  and  proof, 
particularly  to  Professor  J.  B.  Woodworth  of  Harvard 
University,  Mr.  M.  Grant  Daniell  of  Boston,  and  Mrs. 
M.  A.  L.  Lane  of  Hingham.  The  questions  at  the  ends 
of  chapters  have  been  prepared  by  Mr.  R.  H.  Cornish, 
of  the  Girls'  High  School,  New  York,  whose  practical 
acquaintance  with  school  work  insures  their  value. 


W.  M.  D. 


Harvard  University, 
March,  1902. 


CONTENTS 


CHAPTEB  PAGE 

I.  The  Earth  as  a  Globe 1 

II.  The  Atmosphere .  23 

III.  The  Ocean 96 

IV.  The  LaxNds 129 

V.  Plains  and  Plateaus 141 

VI.  Mountains 177 

VII.  Volcanoes 215 

VIII.  Rivers  and  Valleys 234 

IX.  Deserts  and  Glaciers 278 

X.  Shore  Lines 304 

XI.  The  Distribution  of  Plants,  Animals,  and  Man  332 


LIST  OF  PLATES 


I.     Grays  Peak,  Rocky  Mountains  of  Colorado  (photograph 
by  W.  H.  Jackson) Frontispiece 

FACING  PAGE 

II.     A  Sailing  Vessel  at  Sea  (by  Neurdin) 40 

III.  A.  Cumulus  Clouds;  B.  Cirrus  Clouds  (by  Riggenbach)  .      63 

IV.  Waterspout  over  Vineyard  Sound,   Aug.    19,    1896   (by 

J.  N.  Chamberlain) 67 

V.     The  Bore,  or  Surf-like  Flood  Tide,  in  an  Estuary  at  the 

Head  of  the  Bay  of  Fundy,  Nova  Scotia 121 

VI.     The  Great  Plains  (by  W.  D.  Johnson) 158 

VII.     A  Railroad  rounding  a  Spur  of  Mt.  Ouray,  Colorado  (by 

W.  H.  Jackson) 190 

VIII.     Grandfather  Mountain,  North  Carolina  (by  A.  Keith)       .     204 
IX.     A  Water  Gap  in  the  Allegheny  Mountains  (by  Maryland 

Geological  Survey) 211 

X.     Dinant  on  the  Meuse,  Belgium  (by  Neurdin) 258 

XI.     The  Braided  Channels  of  the  River  Var  in  the  Western 

Alps 261 

XII.     Bad  Lands  in  the  Great  Plains,  South  Dakota  (by  N.  H. 

Darton) 283 

XIII.  A  Sand  Dune  rippled  by  the  Wind  (by  G.  K.  Gilbert)      .     287 

XIV.  The  Muir  Glacier,  Alaska  (by  H.  F.  Reid) 292 

XV.     A  Trough-like  Glaciated  Valley  in  the  Western  Alps  (by 

Neurdin) 299 

XVI.     A  Land-tied  Island,  near  Genoa,  Italy  (by  A.  Noack)     .  315 

XVII.     A  Branch  of  Sogne  Fiord,  Norway  (by  A.  Lindahl)     .     .  320 

XVIII.     Forest  in  the  Equatorial  Rain  Belt,  Ceylon     .     .     .     .     .  348 
XIX.     Moab,  an  Irrigated  Settlement  in  Eastern  Utah  (by  L.  M. 

Prindle) ^.     ....  362 

xii 


LIST   OF  FIGURES 

FIG.  PAGE 

1.  Eclipse  of  the  Moon 2 

2.  Height  of  Land  and  Depth  of  Sea 3 

3.  The  Shadow  of  a  Box,  showing  the  Altitude  of  the  Sun      .     .  8 

4.  Meridians  and  Parallels 9 

6.  Latitude  and  Longitude 9 

6.  Mariner's  Compass 18 

7.  Globular  Form  of  Earth  shown  by  Visibility  of  Stars    ...  20 

8.  Mercurial  Barometer 25 

9.  Murage  of  Part  of  a  Schooner,  formed  on  a  Thin  Layer  of  Air  30 

10.  The  Comey  Self-Recording  Thermometer 32 

11.  Illustration  of  an  Isothermal  Line 33 

12.  Chart  of  Mean  Annual  Temperatures 34 

13.  Anemometer 38 

14.  The  Planetary  Circulation  of  the  Atmosphere 40 

15.  Wet- Weather  Streams  of  the  Tarso  Mountains,  Sahara      .     .  42 

16.  Cyclonic  and  Anticyclonic  Areas 45 

17.  Monthly  Positions  of  the  Earth  with  Respect  to  the  Sun     .     .  47 

18.  Chart  of  Mean  Temperatures  for  January 50 

19.  Chart  of  Mean  Temperatures  for  July 50 

20.  Chart  of  Annual  Range  of  Temperature 61 

21.  Diagrams  of  Terrestrial  Winds  for  January  and  July     ...  53 

22.  Winds  of  January 64 

23.  Winds  of  July 66 

24.  January  Monsoons  in  Indian  Ocean 67 

25.  July  Monsoons  in  Indian  Ocean      . 67 

26.  A  Distant  Thunderstorm 65 

27.  Regions  of  Tropical  Cyclones 68 

28.  Chart  of  Mean  Annual  Rainfall .71 

29.  Annual  Rainfall  of  the  United  States 73 

30.  Storm  Tracks  of  the  North  Temperate  Zone  (after  Loomis)     .  79 
81.  Rotation  of  a  Disk  on  a  Rotating  Globe 86 

xiii 


xiv  LIST   OF   FIGURES 

FIG.  PAGE 

32.  Diagram  of  the  Sun's  Midday  Altitude 88 

33.  Diagram  of  Sunrise  and  Sunset  Hours 89 

34.  Water  and  Land  Hemispheres 97 

35.  An  Ocean  Steamship 98 

36.  Sounding  Instrument  and  Water  Bottle 99 

37.  Dredge 99 

38.  A  Vessel  beset  by  Pack  Ice 103 

39.  An  Iceberg 104 

40.  Globigerina  (magnified  100  times) 105 

41.  Section  of  Continental  Shelf 108 

42.  Orbital  Movement  of  Water  in  Waves 109 

43.  Surf 112 

44.  Chart  of  Ocean  Surface  Temperatures  and  Currents  ....  115 

45.  Displacement  of  a  Vessel  by  Currents 116 

46.  Drift  of  Floating  Objects  by  Currents 117 

47.  Low  Tide  in  a  Harbor 120 

48.  The  Tidal  Wave,  or  Bore,  in  the  Seine 121 

49.  Jellyfish  floating  in  Sea  Water 122 

50.  Deep-Sea  Fish,      x  i     .     .     .     . 123 

51.  Deep-Sea  Crustacean,      x  i 123 

52.  Earth  and  Moon 125 

53.  Spring  Tides,  New  Moon 125 

54.  Neap  Tides,  First  Quarter !     .  125 

55.  Spring  Tides,  Full  Moon 125 

56.  Neap  Tides,  Third  Quarter 125 

57.  Variation  of  Tides  for  Two  Weeks      .....'■....  126 

58.  Height  of  Land  and  Depth  of  Sea 132 

59.  A  Quarry  showing  Weathered  Rock 135 

60.  Mountains  bordering  the  Sea 142 

61.  Sample  Map  of  a  Mountainous  Coast  .     .     .     , 142 

62.  Narrow  Coastal  Plain .  144 

63.  Sample  Map  of  a  Narrow  Coastal  Plain 145 

64.  A  Narrow  Coastal  Plain  in  Scotland t     ...  146 

65.  Broad  Coastal  Plain 147 

66.  Coastal  Plain  of  the  Carolinas 148 

67.  A  Truck  Farm  on  the  North  Carolina  Coastal  Plain  ....  149 

68.  A  Belted  Coastal  Plain 150 

69.  Sample  Map  of  Part  of  a  Belted  Coastal  Plain 151 


LIST  OF  FIGURES  xv 

FIQ.  PAOK 

70.  The  Belted  Coastal  Plain  of  Southern  New  Jersey   ....  163 

71.  An  Embayed  Coastal  Plain 164 

72.  Sample  Map  of  an  Embayed  Coastal  Plain 166 

73.  A.  Branch  of  Chesapeake  Bay,  Maryland 167 

74.  Ancient  Coastal  Plain  of  Wisconsin 101 

76.     A  Plateau  in  Arizona 163 

76.  Diagram  of  a  Narrow  Canyon 164 

77.  Diagram  of  a  Widened  Canyon 166 

78.  The  Allegheny  Plateau 168 

79.  Canyon  of  the  Kanawha  River  in  Allegheny  Plateau,  W.  Va.  169 

80.  The  Enchanted  Mesa,  New  Mexico 172 

81.  Broken  Plateaus 173 

82.  Hurricane  Ledge,  a  Dissected  Fault  Cliff 174 

83.  A  Mountain  Peak 178 

84.  Block  Mountains 179 

85.  Mountains  of  Southern  Oregon 180 

86.  A  Dissected  Mountain  Range,  Utah 182 

87.  Diagram  of  the  Jura,  a  Folded  Mountain  Range 184 

88.  Peaks  of  the  Central  Alps 186 

89.  An  Alpine  Peak  of  Slanting  Layers 187 

90.  Path  of  an  Ice  Fall  in  the  Alps 192 

91.  The  Landslide  of  Airolo,  Switzerland 194 

92.  A  Landslide  in  the  Himalayas 196 

93.  The  Himalaya  Mountains 196 

94.  Alluvial  Fans 198 

96.     A  Filled  Valley  with  a  Flat  Floor 199 

96.  A  Terraced  Valley 200 

97.  Railroad  shaken  by  an  Earthquake,  Northeastern  India    .     .  202 

98.  Land  Surface  displaced  by  an  Earthquake,  Japan    ....  203 

99.  The  Piedmont  Belt,  Virginia 206 

100.  Map  of  the  Piedmont  Belt,  Vu-ginia 207 

101.  The  Upland  of  New  England 208 

102.  Valley  of  the  Deerfield  in  the  New  England  Upland      .     .     .  209 

103.  Diagram  of  the  Allegheny  Mountains,  Pennsylvania    .     .     .  210 

104.  Model  of  Embayed  Mountains 211 

105.  Vesuvius  in  Eruption 217 

106.  Monte  Nuovo 218 

107.  Cinder  Cone  and  Lava  Flow,  California .  220 


xvi  LIST  OF  FIGURES 

FIG.  PAGE 

108.  Deception  Island,  a  Volcanic  Caldera  (plan  and  section)   .     .221 

109.  The  Cone  of  Vesuvius  in  the  Caldera  of  Monte  Somma     .     .  221 

110.  Contour  Map  of  Crater  Lake  in  Mt.  Mazama,  Oregon  .     .     .  222 

111.  Excavations  in  Herculaneum 224 

112.  Distribution  of  Volcanoes  and  Coral  Islands 226 

113.  Lava  Flows  on  the  Plateaus  of  Arizona 228 

114.  The  Lava  Plateau  of  Idaho,  Oregon,  and  Washington  .     .     .  229 

115.  Contour  Map  of  Mt.  Shasta,  California 230 

116.  Mt.  Shasta 231 

117.  Map  of  the  Lake  Nicaragua  District 232 

118.  Diagram  of  Cavern  and  Sink  Hole 235 

119.  Section  showing  Ground  Water  in  Rock  Crevices  beneath  a 

Valley 237 

120.  Diagram  of  a  Coastal  Plain  with  Artesian  Wells      ....  238 

121.  A  Geyser 240 

122.  A  Dividing  Ridge  in  the  Mountains  of  Northwest  England   .  242 

123.  Niagara  Falls 248 

124.  Diagram  of  Niagara  River  between  Lakes  Erie  and  Ontario  .  251 

125.  Falls  of  the  Yellowstone  River 252 

126.  Diagram  of  Torrent,  with  Falls  and  Reaches 253 

127.  Valley  of  Yakima  River,  Washington 257 

128.  The  Mohawk  Valley 258 

129.  Outline  Map  of  a  Young  Valley 259 

130.  Diagrams  of  a  Widening  Valley 260 

131.  A  Meandering  River,  Vale  of  Kashmir,  India 262 

132.  A  Meandering  River  on  the  Plain  of  Hungary 263 

133.  Meandering  Channel  and  Oxbow  Lakes  in  the  Flood  Plain 

of  the  Mississippi 264 

134.  The  Valley  of  California 266 

135.  Torrent  Fan  Delta,  Lake  Geneva,  Switzerland 267 

136.  The  Delta  of  the  Mississippi 268 

137.  Diagram  of  a  Narrowed  Spur  in  a  Meandering  Valley  .     .     .  272 

138.  Diagram  of  a  Cut-Off  Spur  in  a  Meandering  Valley      ...  272 

139.  Intrenched  Meanders  of  the  Neckar 273 

140.  Transverse  and  Longitudinal  Streams 274 

141.  Transverse  and  Longitudinal  Valleys 274 

142.  Water  Gap  of  the  Susquehanna  above  Harrisburg,  Pennsyl- 

vania       274 


LIST  OF  FIGURES  xvii 

FIO.  PAOB 

143.  The  Ozark  Plateau,  Missouri 279 

144.  Glaciated  Areas,  Interior  Basins  and  Ocean  Depths      .     .     .  279 

145.  Flood  in  Cherry  Creek,  Denver,  Colorado 282 

146.  Sand  Dunes  in  the  Sahara    . 287 

147.  Lakes  Bonneville  and  Lahontan 289 

148.  Rosegg  Glacier  in  the  Alps 293 

149.  Viesch  Glacier  in  the  Alps 294 

150.  Glacial  Moraines,  Sierra  Nevada,  California 295 

151.  Glaciated  Area  of  the  Northern  United  States 290 

162.     Ice- Worn  Rocks,  Coast  of  Maine 297 

153.  Glacial  Moraines,  North  Dakota 298 

154.  A  Glacial  Bowlder 298 

155.  A  Drumlin,  Massachusetts 299 

156.  A  Side  Valley  hanging  over  the  Valley  of  the  Ticino,  South- 

ern Alps 300 

157.  Lake  in  the  Adirondacks,  New  York 301 

158.  Sea  Cliffs,  Grand  Manan,  New  Brunswick 306 

159.  Diagram  of  a  Lowland  Coast  with  Bluff  and  Sand  Reef    .     .  309 

160.  The  Sea  Cliffs  of  Normandy  (looking  southwest)      ....  311 

161.  Diagram  of  an  Irregular  Shore  Line 312 

162.  Diagram  of  an  Irregular  Shore  Line  with  Cliffed  Headlands 

and  Beached  Bays 312 

163.  Diagram  of  a  Curved  Shore  Line 313 

164.  A  Cliffed  Headland  and  a  Land-Tied  Island 314 

165.  Gibraltar 816 

166.  Diagram  of  a  Group  of  Sea-Cut  Islands 316 

167.  A  Cliffed  Coast  in  Alaska 316 

168.  The  "  Old  Man  of  Hoy  " 317 

169.  The  Coast  Platform  of  Norway 319 

170.  A  Delta  in  a  Norwegian  Fiord 321 

171.  Deltas  of  the  Texas  Coast 322 

172.  A  Mangrove  Tree 324 

173.  A  Fringing  Reef 326 

174.  A  Barrier  Reef 326 

175.  Part  of  the  Great  Barrier  Reef  of  Australia  (as  seen  at  low 

tide,  looking  toward  the  mainland) 326 

176.  Diagram  of  Part  of  a  Barrier  Reef 327 

177.  Diagram  of  Part  of  an  Elevated  Reef  with  a  New  Fringing  Reef  327 


xviii  LIST  OF  FIGURES 

FIO.  PAGE 

178.  Diagram  of  an  Atoll   .     .    ' *  328 

179.  An  Atoll,  or  Coral  Island 329 

180.  Beavers 341 

181.  Caribou 342 

182.  Jaguar 343 

183.  Kangaroo 344 

184.  Cassowary 347 

185.  Dwarfs  in  the  Equatorial  Forest 351 

186.  Eskimo  hunting  Walrus 352 

187.  Stunted  Trees  at  the  Tree  Line  on  the  Slope  of  Pikes  Peak   .  356 

188.  Ibex 356 

189.  The  Yucca,  a  Desert  Tree 360 

190.  El  Kantara  Oasis,  Algerian  Sahara   . 362 


ELEMENTARY 
PHYSICAL  GEOGRAPHY 

CHAPTER  I 
THE  EARTH  AS  A  GLOBE 

1.  Introduction.  —  Physical  geography  treats  of  the 
various. features  of  the  earth  that  influence  the  manner  in 
which  man  lives  upon  it.  Hence  it  must  consider  the 
form  of  the  earth  as  a  whole,  the  climates  of  its  different 
parts,  its  oceans  with  their  waves  and  tides,  and  the  forms 
of  its  lands. 

It  is  the  plan  of  this  book  to  describe  the  more  important 
kinds  of  physical  features  on  the  earth,  to  refer  them  to 
their  causes  in  natural  processes,  and  to  trace  them  to  their 
consequences  as  seen  in  the  condition  of  mankind. 

2.  The  Shape  of  the  Earth.  —  The  people  of  savage  races, 
when  they  think  at  all  about  the  shape  of  the  earth,  gen- 
erally imagine  it  to  be  a  great  plain,  varied  by  hills  and 
mountains  and  surrounded  by  the  sea;  for  that  is  the 
appearance  of  the  lands  when  seen  from  some  high  point, 
with  mountains  rising  to  greater  heights,  lowlands  extend- 
ing to  the  seashore,  and  the  ocean  stretching  beyond. 

The  people  of  an  ignorant  race  usually  regard  the  place 
where  they  live  as  the  center  of  the  great  earth  plain.     Of 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


the  ocean  they  know  little ;  its  further  parts  are  invisible 
and  mysterious  and  are  often  thought  of  as  much  more 
dangerous  than  those  which  border  the  solid  lands. 

Among  the  earliest  observations  that  led  to  a  knowledge 

of  the  true  form  of  the  earth  were  those  made  by  the  Greeks. 

The  great  philosopher  Aristotle,  who  flourished  about 

the  middle  of  the  fourth  century  B.C.,  made  an  ingenious 

use  of  the  eclipses  of  the 
moon  to  determine  the  form 
of  the  earth.  He  knew  that 
the  earth  cast  a  great  shadow 
stretching  away  into  space  on 
the  side  opposite  the  sun;  and 
that  whenever  the  moon,  in 
its  movement  around  the 
earth,  entered  this  shadow 
it  was  hidden  or  eclipsed, 
because  it  then  no  longer 
received  the  sunlight  that 
ordinarily  makes  it  visible. 
He  noted  that  the  edge  of 
the  earth's  shadow  on  the 
moon  is  a  curved  line,  and  thus  he  knew  that  the  earth 
must  have  a  curved  surface,  such  as  a  globe  has. 

The  moon,  revolving  about  the  earth  once  in  twenty- 
eight  days,  is  not  eclipsed  every  time  it  is  opposite  the 
sun,  for  it  usually  passes  a  little  to  one  side  of  the  earth's 
tapering  shadow. 

The  familiar  argument  for  the  globular  form  of  the 
earth,  based  on  the  disappearance  of  the  lower  part  of 


Fig.  1.  Eclipse  of  the  Moon,  show- 
ing the  Curved  Edge  of  the  Earth's 
Shadow 


THE  EARTH  AS  A  GLOBE  3 

distant   vessels   at   sea,  was   not   mentioned   by   ancient 
writers  until  about  the  beginning  of  the  Christian  era. 

3.  Size  of  the  Earth.  —  The  earliest  recorded  measure- 
ment of  the  size  of  the  earth  was  made  by  a  Greek  philos- 
opher in  the  third  century  B.C.,  who  found  its  diameter  to 
be  about  8000  miles.  The  knowledge  thus  gained  by  the 
wise  men  of  the  ancient  Mediterranean  countries  concern- 
ing the  size  and  shape  of  the  earth  was  unknown  to  the 
rest  of  the  world  and  was  afterwards  forgotten ;  but  it  was 
regained  about  the  time  of  Columbus. 

The  proof  of  globular  form  by  sailing  around  the  earth, 
or  circumnavigation,  was  first  accomplished  in  the  sixteenth 


Fig.  2.    Height  of  Land  and  Depth  of  Sea  compared  to  Curvature  of 
Earth's  Surface 

century,  when  the  Philippine  islands  were  discovered. 
What  can  you  learn  about  Magellan  ?  In  later  centuries 
nearly  all  parts  of  the  earth  have  been  explored,  and  its 
size  and  shape  have  been  accurately  measured.  Its  diam- 
eter is  about  79t2  miles. 

4.  Unevenness  of  the  Earth's  Surface.  —  The  broad 
depressions  between  the  continents,  in  which  the  oceans 
are  gathered,  are  of  small  depth  compared  to  the  diameter 
of  the  earth.  The  continents  have  many  mountains  and 
valleys,  but  the  general  surface  of  the  lands  does  not 
depart  greatly  from  a  globular  form,  such  as  is  so  well 
shown  by  the  surface  of  the  oceans.     This  is  fortunate, 


4  ELEMENTARY  PHYSICAL  GEOGRAPHY 

for  on  very  uneven  lands  the  long  ascents  and  descents 
between  the  higher  and  lower  parts  would  make  travel 
and  transportation  enormously  difficult  or  utterly  impos- 
sible. It  is  difficult  enough  to  cross  over  the  existing 
mountain  ranges,  whose  highest  peaks  rise  hardly  more 
than  1  oV^  of  the  earth's  radius  and  whose  passes  are  much 
lower ;  if  their  height  were  j^q-q  of  the  earth's  radius,  they 
would  be  absolutely  im_passable. 

Exercise.  With  chalk  and  string  draw  a  circular  curve  of  4  feet 
radius  on  a  blackboard.  If  the  chalk  line  is  ^q  inch  wide,  it 
will  represent  the  average  depth  of  the  oceans  (2  miles)  ;  if  it  is 
increased  underneath  here  and  there  to  -^  inch,  it  will  indicate 
the  greatest  known  depths  of  the  oceans  (about  5  miles).  Small 
inequalities  rising  j^^  to  -^^  inch  above  the  outside  of  the  curved 
line  will  represent  the  altitude  of  the  continents  and  their  moun- 
tains above  sea  level.  At  a  distance  of  20  feet  the  departure  of 
the  curve  from  a  true  circle  will  be  hardly  noticed.  So  the  earth 
would  seem  smooth  and  truly  globular  if  we  could  see  it  from  a 
great  distance. 

5.  Consequences  of  the  Size  and  Shape  of  the  Earth.  — 
The  earth  is  so  large  that  savage  tribes,  even  on  the  same 
continent,  may  remain  in  ignorance  of  each  other  for  cen- 
turies. Each  tribe  then  comes  to  have  its  own  way  of 
doing  things,  appropriate  to  its  local  surroundings.  Thus 
differences  of  language  and  customs  have  originated.  But 
since  railroads  and  steamships  have  been  invented  the 
earth  may  be  considered  a  relatively  small  body ;  an  active 
traveler  may  now  visit  nearly  all  its  larger  districts  in  his 
adult  years. 

The  civilized  nations  have  become  well  acquainted  with 
each  other,  because  the  earth's  surface  is  so  nearly  level 


THE  EARTH  AS  A  GLOBE  6 

that  movement  over  it  is  possible.  They  now  maintain  an 
international  postal  service,  by  which  nearly  200,000  post 
offices  are  in  regular  communication  with  each  other.  The 
Roman  alphabet  is  used  by  many  nations,  although  their 
language  may  be  different.  The  use  of  Arabic  numerals 
is  even  more  extended.  The  metric  system  of  weights 
and  measures  is  already  widely  introduced  and  will 
probably  be  adopted  by  all  advanced  nations  during  this 
century. 

The  products  of  remote  regions  are  exchanged,  even 
from  opposite  sides  of  the  earth.  The  wheat  of  one 
continent  furnishes  flour  to  another.  Australian  wool 
and  meat  are  sold  in  London.  The  manufactures  of 
Europe  and  the  United  States  are  distributed  all  over  the 
world.  On  a  more  uneven  earth  it,  might  be  impossible 
to  develop  a  world-wide  conunerce. 

6.  The  Earth's  Attraction,  or  Gravity It  is  the  attrac- 
tion of  the  earth,  or  terrestrial  gravity,  that  causes  bodies 
to  have  weight  and  to  fall  when  not  supported.  Recog- 
nizing the  earth  to  be  a  globe,  "down"  is  toward  its 
center,  or  in  the  direction  that  bodies  are  pulled  by  its 
attraction,  as  indicated  by  a  plumb  line;  "up"  is  away 
from  the  earth's  center,  or  against  the  pull  of  gravity.  A 
level  surface,  like  that  of  a  quiet  body  of  water,  a  calm 
lake  or  ocean,  represents  a  part  of  the  convex  or  globular 
surface  of  the  earth;  it  is  everywhere  at  right  angles  to 
the  up-and-down,  or  vertical,  lines. 

The  stems  and  trunks  of  plants  grow  "up"  against  the 
force  of  gravity.     Even  on  hill^des  trees  tend  to  grow 


6  ELEMENTARY  PHYSICAL  GEOGRAPHY 

erect  and  not  square  out  from  the  sloping  surface.  Many 
parts  of  the  skeletons  of  men  and  animals,  as  well  as  many 
of  their  muscles,  are  especially  adapted  to  bear  the  strain 
that  is  exerted  upon  them  by  the  downward  weight  of  the 
body.  The  habit  of  lying  down  to  sleep  has  been  formed 
chiefly  to  rest  the  muscles  that  are  in  action  while  a  per- 
son is  standing.  The  walls  of  buildings  are  built  vertical, 
because  in  that  position  they  will  stand  most  securely. 

7.  The  Earth's  Rotation  and  its  Consequences.  —  Few 
discoveries  ever  made  by  man  have  been  more  opposed  to 
his  early  beliefs  than  that  the  earth  turns  or  rotates  on  its,. 
axis  once  a  day  and  that  it  moves  or  revolves  around  the 
sun  once  a  year;  for  nothing  is  more  natural  than  to  sup- 
pose that  the  firm  earth  stands  still  in  the  center  of  the 
universe  and  that  all  the  bodies  of  the  sky  turn  around  it. 
But  it  has  been  proved  that  the  apparent  turning  of  the 
sun  and  stars  around  the  earth  from  east  to  west  is  due  to 
the  actual  rotation  of  the  earth  from  west  to  east.  One 
may  gain  a  false  impression  of  the  same  kind  while  look- 
ing from  the  window  of  a  smoothly  running  train,  when  it 
seems  as  if  the  landscape  moved  backward  instead  of  the 
train  forward.  The  northern  end  of  the  imaginary  line, 
or  axis,  on  which  the  earth  turns  is  directed  (almost) 
toward  the  North  Star  in  the  sky. 

A  little  over  two  centuries  ago  it  was  discovered  that 
the  earth  is  not  a  perfect  sphere,  but  is  very  slightly  flat- 
tened at  the  poles.  The  equatorial  diameter  is  7926  miles ; 
the  polar  diameter,  7900  miles.  This  was  explained  by 
Newton  as  a  result  of  the  earth's  rotation,  and  it  may  be 


THE  EARTH  AS  A  GLOBE  7 

taken  as  one  of  the  best  proofs  that  the  earth  and  not 
the  sky  turns. 

8.  Day  and  Night.  —  The  sun  illuminates  one  half  of 
the  earth,  leaving  the  other  half  in  shadow.  As  the  earth 
turns  around,  passing  from  the  light  into  the  darkness,  one 
perceives  the  succession  of  day  and  night  every  time  a 
rotation  is  made.  The  time  at  which  the  sun  comes  in 
sight  over  the  eastern  horizon  is  sunrise;  when  it  disap- 
pears below  the  western  horizon,  sunset. 

The  succession  of  day  and  night,  resulting  from  the 
rotation  of  the  earth,  has  given  man  and  many  animals 
the  habit  of  working  in  the  light  and  resting  in  the  dark- 
ness. The  period  of  the  earth's  rotation  furnishes  a  nat^ 
ural  unit  of  time,  easily  recognized  and  counted,  and 
everywhere  alike  and  constant.  Clocks  and  watches  are 
regulated  to  keep  time  with  the  earth's  turning.  The 
hour  hand  of  timepieces  in  common  use  turns  once  for  the 
average  duration  of  daylight,  and  once  for  the  average 
duration  of  darkness. 

The  rotation  of  the  earth,  causing  sunrise  and  sunset, 
suggests  a  natural  system  of  directions  by  which  the  rela- 
tive positions  of  different  places  may  be  indicated.  The 
cardinal  points,  east  and  west,  north  and  south,  are  in  a 
more  or  less  definite  way  recognized  by  most  peoples  of 
the  world. 

The  sun  rises  through  the  eastern  half  of  the  sky  dur- 
ing the  morning  and  sinks  through  the  western  half  in  the 
afternoon.  Midday  is  the  moment  when  the  sun  passes 
the  north  and  south  line  that  divides  the  eastern  from 


8 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


the  western  half  of  the  sky.  The  sun  then  reaches  its 
greatest  height  above  the  horizon;  and,  hence,  at  this 
moment  a  vertical  rod  casts  the  shortest  shadow. 

Exercise.  Set  up  a  vertical  post'  in  level  ground  (or  a  square- 
cornered  box  on  a  level  table).  Mark  the  successive  positions  of  the 
end  of  the  rod  shadow  (or  of  a  corner  of  the  box  sshadow)  every  ten 
or  fifteen  minutes  for  an  hour  or  more  before  and  after  noon.     Draw 


iiiiiiiiiiiiiiiiiiiniiiiiiiiiiiiimiiiMMiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiunniiiiiiiiniiiiiuiiiiiiii 


Fig.  3.    The  Shadow  of  a  Box,  showing  the  Altitude  of  the  Sun 

a  line  through  the  marks.  Find  the  shortest  line  from  the  base  of 
the  post  (or  from  the  lower  corner  of  the  box)  to  the  line  through 
the  marks.  This  shortest  line  is  a  true  north  line,  or  meridian  (mid- 
day) line.  On  the  following  day  note  the  moment  when  the  shadow 
falls  on  the  meridian  line  ;  that  moment  is  local  solar  noon,  or  mid- 
day.    A  watch  then  set  to  12  o'clock  will  mark  local  solar  time. 

9.    Latitude  and  Longitude The  north  or  meridian 

line  would,  if  followed  in  the  direction  awaj  from  the 


THE  EARTH  AS  A  GLOBE 


9 


sun,  lead  to  the  north  pole  ;  in  the  opposite  direction,  to  the 
south  pole.  All  meridian  lines  therefore  meet  at  the  poles. 
When  prolonged  around  the  earth  they  are  called  meridian 
circles.  Lines  drawn  at  right  angles  to  the  meridians  will 
run  parallel  to  each  other,  east  and  west,  around  the  earth 
and  are  therefore  called  parallels.  The  earth  being  globu- 
lar, a  simple  system  of  meridians  and  parallels  may  be 
imagined  to  form  a  network  of  circles  over  its  surface.  •# 


•KarthPbU 


Fig.  4.    Meridians  and  Parallels 


Fig.  5.    Latitude  and  Longitude 


It  is  by  reference  to  these  lines  that  the  relative  positions 
of  places  on  the  earth's  surface  are  determined. 

The  parallel  that  lies  halfway  between  the  poles  is 
called  the  equator.  It  divides  the  earth  into  the  northern 
and  southern  hemispheres  (half-spheres).  The  latitude  of 
a  place  is  its  distance  north  or  south  of  the  equator.  It  is 
measured  along  the  meridian  of  the  place  and  is  counted 
in  degrees,  ninety  to  a  quarter  circle.  In  Figure  5  the  lati- 
tude of  A  is  the  number  of  degrees  in  the  arc  AC,  or  the 
angle  AOC.     What  is  the  latitude  oi  B? 


10  ELEMENTARY  PHYSICAL  GEOGRAPHY 

Low  latitudes  are  near  the  equator  in  either  hemi- 
sphere; high  latitudes,  near  the  poles;  middle  latitudes, 
roughly  midway  between  pole  and  equator  in  either  hemi- 
sphere.    (See  page  89.) 

The  longitude  of  a  place  is  the  number  of  degrees  by 
which  its  meridian  is  east  or  west  of  a  standard  or  prime 
meridian.  The  meridian  of  the  national  observatory  of 
Great  Britain  at  Greenwich,  a  suburb  of  London,  is  now 
very  generally  taken  as  the  standard.  The  longitude  of  a 
place  is  measured  from  the  prime  meridian  east  or  west 
along  the  equator  to  the  meridian  of  the  place  and  is 
counted  in  degrees,  180  to  half  a  circle,  or  in  hours, 
12  to  a  half  circle.  If  NACS^  Figure  5,  is  taken  as  the 
standard  or  prime  meridian,  the  longitude  of  B  is  measured 
by  the  arc  CD  of  the  equator,  or  by  the  angle  (70Z>, 
between  the  local  and  the  prime  meridians.  Is  B  in  east 
or  west  longitude  ?  What  is  the  latitude  of  G  ?  What 
is  its  longitude  ? 

Practical  Exercise.  A  useful  illustration  of  the  manner  in  which 
maps  are  made  is  given  by  providing  a  number  of  outline  maps, 
showing  parallels  and  meridians  (latitude  and  longitude  lines),  on 
which  the  latitudes  and  longitudes  of  a  number  of  points  are  to  be 
platted.  The  points  should  be  selected  on  the  boundary  of  some 
state  or  country ;  their  positions  may  be  taken  from  an  atlas  and 
written  upon  a  blackboard.  By  drawing  a  line  through  the  points 
thus  platted  each  pupil  will  have  constructed  a  rough  map  of  the 
chosen  boundary.     Rivers  and  cities  may  be  similarly  located. 

Land  surveys,  by  which  the  boundary  lines  of  farms 
and  house  lots  are  marked  out,  are  best  made  with  refer- 
ence to  the  local  meridian,  or  north  line.     Navigators  have 


THE  EARTH  AS  A  GLOBE  11 

daily  occasion  to  determine  their  position  with  respect  to 
the  network  of  meridians  and  parallels,  in  order  to  follow 
the  desired  route,  to  avoid  islands  and  headlands,  and  to 
reach  their  intended  port. 

The  boundaries  of  thinly  settled  pai*ts  of  civilized 
nations  arid  states  are  often  defined  by  meridians  and 
parallels,  as  between  the  western  parts  of  the  United 
States  and  Canada,  as  well  as  between  many  of  the  states 
themselves,  and  between  the  various  parts  of  Canada  and 
Australia.  Thus  great  advantage  is  taken  of  the  simple 
globular  form  and  regular  rotation  of  the  earth. 

10.  Relation  of  the  Earth  to  the  Sun. — The  sun,  glow- 
ing with  extreme  heat,  has  the  enormous  diameter  of 
866,500  miles.  If  the  earth  were  placed  at  the  sun*s 
center,  and  the  moon  were  moving  around  the  earth  at  its 
actual  distance  of  240,000  miles,  the  sun  would  still  reach 
almost  200,000  miles  beyond  the  moon  on  all  sides. 

So  huge  a  body  is  a  fitting  center  for  the  earth  to  move 
around.  Even  at  the  great  distance  of  93,000,000  miles, 
the  brilliant  sun  gives  abundant  heat  and  light  to  the 
earth.  This  distance  is  so  great  that  an  express  train 
traveling  from  the  earth  fifty  miles  an  hour  could  not 
reach  the  sun  in  less  than  two  centuries. 

The  earth  travels  or  revolves  around  the  sun  every  year 
in  a  nearly  circular  path,  called  its  orbit.  In  order  to 
accomplish  this  long  journey  of  over  600,000,000  miles, 
our  globe  rushes  along  at  a  speed  of  18.5  miles  a  second, 
or  over  1,500,000  miles  a  day.  As  the  motion  is  accom- 
plished with  perfect  smoothness,  and  as  we  move  with  the 


12  ELEMENTARY  PHYSICAL  GEOGRAPHY 

earth,  we  are  as  unconscious  of  this  rapid  movement  in 
the  annual  orbit  as  we  are  of  the  diurnal  rotation  on  the 
axis. 

Exercise.  Lay  a  large  sheet  of  paper  on  a  table;  draw  a  line 
through  the  middle  of  the  sheet.  Let  this  line  represent  a  distance  of 
200,000,000  miles.  On  each  side  of  the  middle  of  the  line  set  up  a 
pin,  so  that  the  distance  between  the  pins  shall  represent  3,000,000 
miles  (^^  of  the  length  of  the  Une).  Lay  off  189,000,000  miles  on 
this  scale  on  a  thread  and  knot  together  the  ends  of  this  length,  so 
as  to  make  a  loop.  Lay  the  loop  over  the  pins,  stretch  it  tight  with 
a  pencil  point,  and  thus  guided  draw  a  curve  around  the  pins.  The 
line  thus  drawn  is  nearly  circular  and  represents  the  true  form  of 
the  earth's  orbit.  Take  out  the  pins.  Around  one  pin  hole  draw  a 
circle  to  scale,  somewhat  less  than  1,000,000  miles  in  diameter; 
this  will  represent  the  sun.  On  the  same  scale  the  earth  would  be  a 
small  dot.  The  points  where  the  orbit  is  crossed  by  the  middle 
line  show  the  greatest  and  least  distances  of  the  earth  from  the  sun. 
What  are  these  distances?  The  point  nearest  the  sun  (perihelion= 
"near-sun")  is  passed  on  January  1 ;  the  farthest  (aphelion=" far- 
sun")  on  July  1. 

The  stars  are  distant  suns,  shining  by  their  own  light. 
Most  of  them  are  much  more  than  a  million  times  as  far 
from  the  sun  as  the  earth  is.  They  are  so  exceedingly- 
remote  that  a  ray  of  light  which  travels  from  the  sun  to 
the  earth  in  eight  minutes  would  be  about  three  and  a 
half  years  on  the  journey  to  us  from  the  nearest  star. 
Many  of  the  stars  are  believed  to  be  larger  than  the  sun. 

11.  Relation  of  the  Earth  to  other  Planets.  —  There  are 
a  number  of  other  bodies  which,  like  the  earth,  move 
around  the  sun.  Like  the  earth  they  do  not  shine  by 
their  own  light,  but  only  by  sunlight  that  falls  on  them. 


THE  EARTH  AS  A  GLOBE  18 

At  night  these  bodies  look  like  stars,  except  that  they 
twinkle  less.  Their  light  is  brighter  or  fainter  accord- 
ing to  their  size  and  their  distance  from  the  sun.  The 
telescope  shows  them  to  be  of  globular  form,  like  the 
earth.  Their  movement  among  the  stars,  easily  noted 
from  month  to  month,  shows  that  they  revolve  around  the 
sun  in  the  same  direction  that  the  earth  does.  The  spots 
that  may  sometimes  be  seen  on  the  sun  show  that  it  also 
rotates  on  its  axis  in  a  little  less  than  a  month,  in  the  same 
direction  that  the  planets  move  around  it. 

The  planets  that  may  be  easily  seen  without  a  telescope 
are  named  Mercury,  Venus,  Mai-s,  Jupiter,  and  Saturn. 
Mercury,  Venus,  and  Mars  are  smaller  than  the  earth; 
Jupiter  and  Saturn  are  much  larger.  Mercury  and  Venus 
are  nearer  to  the  sun  than  the  earth  is ;  Mars,  Jupiter,  and 
Saturn  are  more  distant;  and  two  other  large  planets, 
Uranus  and  Neptune,  are  farther  away  than  Saturn.  The 
planets  that  are  near  the  sun  revolve  around  it  in  a  shorter 
time  (or  "year")  than  those  further  away.  The  small 
planets.  Mercury  and  Venus,  are  believed  to  rotate  very 
slowly  on  their  axes,  so  that  their  "day"  is  long.  The 
large  planets,  Jupiter  and  Saturn,  rotate  rapidly,  so  that 
their  day  is  about  half  as  long  as  ours. 

The  moon  is  a  planetlike  body  which  revolves  around 
the  earth  while  the  earth  revolves  around  the  sun.  The 
moon  is  therefore  called  a  satellite  (=  a  follower),  because 
it  accompanies  the  earth.  Its  diameter  is  about  a  quarter 
of  that  of  the  earth;  its  distance  from  the  earth  is  about 
240,000  miles.  Mercury  and  Venus  have  no  satellites,  Mars 
has  two  very  small  ones,  Jupiter  has  five,  Saturn  has  eight. 


14 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


It  is  thus  found  that  the  earth  is  not  a  solitary  body, 
unlike  all  others,  but  that  it  occupies  an  intermediate  posi- 
tion in  a  large  family  of  similar  bodies. 

Diagrams  may  be  constructed  to  represent  the  relative 
sizes  of  the  planets  and  their  relative  distances  from  the 
sun  by  means  of  the  following  table.  Diameters  are  given 
in  thousands  of  miles ;  distances  in  millions  of  miles. 


Distance 

Diameter 

Distance 

Diameter 

Sun 

0 

866. 

Jupiter    .  . 

480 

85.3 

Mercury    .  . 

36 

3.0 

Saturn  .  .  . 

881 

70.1 

Venus     .  .   . 

67 

7.6 

Uranus    .  , 

1772 

30.9 

Earth  .... 

93 

7.9 

Neptune  .  . 

2770 

34.0 

Mars    .... 

141 

4.2 

12.  The  Solar  System.  —  The  sun,  the  planets,  and  their 
satellites  form  a  group  of  bodies  called  the  solar  system. 
The  resemblances  of  form  and  motion  among  the  planets 
and  satellites  are  so  numerous  that  it  is  believed  that  they 
have  all  had  a  common  origin.  It  has  been  thought  that 
these  bodies,  and  the  sun  also,  have  been  formed  by  the 
gathering  together  of  materials  that  were  once  scattered 
through  an  enormous  space,  like  a  vast  cloud  or  nebula. 
This  interesting  and  famous  theory  is  called  the  nebular 
hypothesis,  but  it  is  not  successful  in  explaining  all  fea- 
tures of  the  solar  system. 

The  stars  resemble  the  sun  in  many  ways.  It  is 
believed  that  each  star  may  be  accompanied  by  a  larger  or 
smaller  family  of  planets ;  and  hence  the  number  of  earth- 
like  bodies  in  the  universe  is  probably  very  large. 


THE  EARTH  AS  A  GLOBE  15 

13.  Structure  of  the  Earth.  —  Rocks  of  one  kind  or 
another  are  often  seen  at  the  surface  of  the  lands;  or  if 
the  surface  is  covered  by  soil,  rocks  may  be  found  beneath 
the  soil  in  wells  and  railroad  cuts.  The  deepest  mines 
and  borings,  reaching  about  a  mile  beneath  the  surface, 
pass  through  similar  rocky  materials.  Hence  it  is  believed 
that  the  body  of  the  earth  is  composed  of  rock. 

This  great  globe  of  rock  is  covered  Avith  a  considerable 
quantity  of  water  and  air  lying  upon  its  surface  and 
forming  its  oceans  and  its  atmosphere.  The  oceans  are 
not  continuous  all  over  the  earth,  but  are  gathered  on 
the  lower  parts  of  the  surface,  while  the  higher  parts  rise 
somewhat  above  the  oceans  and  form  the  continents.  The 
atmosphere  entirely  incloses  the  oceans  and  the  continents, 
extending  far  above  the  highest  mountains. 

Thus  the  earth  as  a  whole  consists  of  matter  in  three 
different  states,  —  solid,  liquid,  and  gaseous.  The  liquid 
portion,  or  water,  is  also  known  as  a  solid  when  it  freezes 
and  forms  ice ;  and  as  a  gas  when  it  evaporates  and  mixes 
with  the  air  as  invisible  water  vapor.  The  solid  portion, 
or  rock,  is  seen  as  a  liquid  when  it  comes  forth  from  vol- 
canoes at  high  temperatures  as  molten  lava.  The  gaseous 
portion,  or  air,  is  always  gaseous  under  natural  conditions, 
but  it  may  be  artificially  reduced  to  a  liquid  or  a  solid  by 
subjecting  it  to  heavy  pressure  at  extremely  low  tempera- 
tures. 

There  is  a  certain  amount  of  mixture  of  rock,  water, 
and  air,  or  of  the  solid,  liquid,  and  gaseous  parts  of  the 
earth.  Some  solid  substances  have  been  dissolved  by  the 
action  of  water  and  are  now  found  in  the  oceans.    A  small 


16  ELEMENTARY  PHYSICAL  GEOGRArHY 

amount  of  rock  in  very  fine  particles,  or  dust,  is  raised 
from  barren  surfaces  by  the  wind  and  carried  far  and 
wide ;  the  finest  particles  remain  long  in.  the  air,  slowly 
settling  but  often  lifted  again  by  rising  currents.  Water 
and  air  penetrate  all  pores  and  crevices  that  they  can  find 
in  the  rocky  sphere.  Water  vapor  is  always  present  in 
the  atmosphere  in  small  and  variable  proportion ;  it  becomes 
visible  when  chilled  and  condensed,  forming  small  liqui4 
or  solid  particles  in  cloud,  rain,  or  snow.  A  small  amount 
of  air  is  dissolved  in  the  oceans ;  but  for  this,  the  fish  and 
many  other  animals  that  live  beneath  the  surface  of  the 
sea  could  not  breathe. 

14.  Underground  Temperatures.  —  Temperatures  meas- 
ured in  deep  wells  and  mines  show  that  the  earth  becomes 
warmer  beneath  the  surface.  The  average  increase  of 
temperature  downwards  is  about  1°  for  sixty  feet.  At 
great  depths,  such  as  twenty  or  a  hundred  miles  or  more, 
very  high  temperatures  would  be  expected ;  they  are  proved 
to  occur  by  the  melted  lavas  that  rise  and  escape  in  vol- 
canoes. It  is  therefore  supposed  that  the  great  interior 
rocky  mass  of  the  earth  is  hot  enough  to  be  melted, 
although  the  enormous  pressure  of  the  outer  parts  may 
prevent  the  expansion  that  would  be  needed  to  make  it 
liquid.  It  may  thus  be  forced  to  remain  solid  in  spite  of 
its  high  temperature.  The  outer  and  cooler  part  of  the 
earth  is  often  called  its  crust. 

Just  as  a  hot  ball  of  iron  will  cool  when  it  is  hung  in 
the  free  air,  so  the  earth  must  be  slowly  cooling  as  it 
moves  through  cold  space.     It  is  very  probable  that  the 


THE  EARTH  AS  A  GLOBE  17 

unevenness  of  the  geosphere,  in  ocean  basins,  continents, 
and  mountains,  is  in  some  way  the  result  of  a  sort  of  8et> 
tling  and  bending  of  the  crust,  slowly  caused  by  the  long 
cooling  of  the  earth. 

15.  Age  of  the  Earth.  —  It  is  impossible  to  say  what  the 
age  of  tlie  earth  and  the  solar  system  is,  but  it  certainly 
should  be  reckoned  in  millions  and  millions  of  years. 
There  is  every  reason  to  believe  that  the  sun  and  the 
planets  existed  for  .an  indefinitely  long  period  before  the 
condition  of  the  earth's  surface  was  such  as  to  allow 
the  habitation  of  the  planet  by  plants  and  animals.  It  is 
well  proved  by  the  prints  or  fossils  of  various  plants  and 
animals  in  ancient  rock  layers  that  these  lower  forms  of 
life  existed  upon  the  earth  for  a  vast  length  of  time, 
millions  and  millions  of  years  before  man  appeared.  It 
seems  entirely  possible  that  other  planets  may  have  once 
been,  may  now  be,  or  may  yet  come  to  be  occupied  by 
inhabitants  of  some  kind. 

16.  The  Earth  as  a  Magnet. — If  a  magnetized  bar  of  steel 
is  balanced  on  a  pivot  and  placed  in  the  neighborhood  of  a 
large  magnet,  the  direction  in  which  the  small  bar  points 
will  be  determined  by  its  large  neighbor.  This  may  be 
tested  by  changing  the  relative  positions  of  the  two.  If  the 
small  magnet  is  left  alone,  it  will  in  most  parts  of  the  earth 
turn  until  it  points  about  north  and  south.  This  is  because 
the  earth  acts  as  if  it  were  a  huge  magnet  and  so  determines 
the  direction  in  which  smaller  magnets  tend  to  stand. 

The  behavior  of  suspended  bar  magnets  makes  them 
very   valuable    in   determining    directions,    especially   in 


18 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


cloudy  weather  at  sea.  A  magnet  mounted  in  a  con- 
venient case  is  called  a  compass,  the  bar  being  called  a 
needle.  In  the  mariner's  compass  a  card  bearing  the 
letters  indicating  the  points  of  the  compass  lies  on  the 
needle  and  turns  with  it. 

The  needle  seldom  points  along  a  true  meridian  toward 
the  pole,  but  somewhat  to  one  side  or  the  other  of  a 
meridian,  in  a  direction  that  if  followed  will  lead  toward 
the  "  north  magnetic  pole  "  (about  twenty  degrees  away 

froiji  the  true  north  pole 
toward  Hudson  bay)  or 
toward  the  "south  mag- 
netic pole  ^'  (about  the 
same  distance  from  the 
true  south  pole  toward 
New  Zealand).  The  dif- 
ference between  true 
north  and  magnetic 
north  at  any  place  may 
be  determined  by  com- 
paring the  direction  of  the  midday  (or  shortest)  shadow 
cast  by  a  vertical  pole  with  the  direction  of  a  compass 
needle. 


Fig.  6.    Mariner's  Compass 


17.  The  Aurora.  —  During  clear  nights,  especially  in 
winter  time,  the  northern  part  of  the  sky  is  sometimes 
illuminated  by  an  arch  of  whitish,  greenish,  or  rosy  light. 
Moving  streamers  of  light,  whitish  or  colored,  are  seen 
between  the  arch  and  the  higher  parts  of  the  sky.  This 
appearance  is  called   the   aurora   borealis,.  or  "northern 


THE  EARTH  AS  A  GLOBE  19 

lights."  The  aurora  is  more  frequent  and  brilliant  in 
high  northern  latitudes  than  in  temperate  latitudes.  A 
similar  appearance  in  far  southern  latitudes  is  known  as 
the  aurora  australis.  In  both  cases  the  middle  of  the 
auroral  arch  is  seen  in  the  direction  of  the  magnetic  pole. 
From  the  disturbance  of  delicate  magnets  during  an 
auroral  display  it  is  believed  that  the  lights  are  due  to  a 
faint  electric  discharge  controlled  by  the  magnetic  forces 

of  the  earth. 

• 

Supplement  to  Chapter  I 

18.  Proof  of  the  Globular  Form  of  the  Earth  by  Observations  of  the 
Stars.  —  Looking  upward  from  the  earth,  the  sky  seems  like  a  hollow 
shell  of  vast  size,  carrying  the  sun  by  day  and  the  stars  by  night. 
The  earth  may  be  thought  of  as  standing  at  the  center  of  the  great 
sky  shell,  so  that  an  observer  at  any  point  sees  only  half  the  sky 
above  him,  the  other  half  being  hidden  beneath  the  earth.  The 
lower  border  of  the  visible  half  of  the  sky  is  called  the  horizon,  and 
the  plane  that  extends  outward  from  the  observer  to  the  sky  border 
is  called  the  plane  of  the  horizon. 

By  watching  through  the  night  the  Greek  philosophers  saw  the 
stars  rising  in  the  eastern  side  of  the  sky  and  descending  in  the 
western;  and  they  concluded  that  the  sky,  carrying  the  stars  with 
it,  turned  around  the  earth  once  a  day.  It  is  now  known  that  the 
earth  turns,  and  not  the  sky. 

In  order  to  understand  this  clearly  the  pupil  should  learn  by 
observation  something  of  the  diurnal  movement  of  the  sun,  moon, 
and  stars  across  the  sky  and  should  recognize  that  their  paths  are 
parts  of  slanting  circles. 

Perception  of  the  essential  facts  is  greatly  aided  by  the  use  of  a 
"pointer,"  three  or  four  feet  long,  tied  at  one  end  to  the  top  of  a 
stake  about  which  it  may  turn  freely.  Direct  the  pointer  toward  the 
sun  at  different  hours  of  the  day.     Repeat  this  until  the  (apparent) 


20 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


movement  of  the  sun  becomes  familiar.  Then  sweep  the  pointer 
more  rapidly  through  its  successive  positions.  Infer  the  directions 
it  would  assume  if  the  sun  could  be  observed  all  night.  Infer  the 
attitude  of  a  line,  or  axis,  about  which  the  pointer  turns.  This  line 
must  be  parallel  to  the  axis  on  which  the  earth  turns. 

The  (apparent)  diurnal  rotation  of  the  stars  is  best  shown  by  home 
observations.  Direct  a  pointer  toward  a  star  at  a  convenient  evening 
hour.  Watch  the  star  for  five  or  ten  minutes  and  note  its  change  of 
position.  The  next  evening  begin  the  observation  fifteen  or  twenty 
minutes  earlier.     How  can  the  facts  thus  observed  be  best  accounted 

for?     The  movement  of 
^^  ^^      *    "         the  stars  as  seen  from  dif- 

ferent places  must  next 
be  considered. 

When  one  travels 
southward  from  B  to  C 
it  is  found  that  new 
groups  of  stars,  Z, 
Figure  7,  not  visible 
before,  come  into  sight 
over  the  southern  horizon,  while  other  groups.  A',  that  had  before 
been  seen  over  the  northern  horizon  are  no  longer  visible.  From 
this  it  is  concluded  that  the  plane  of  the  horizon  HJ  at  the  new 
point  of  observation  is  not  parallel  to  the  plane  FG  at  the  first 
point,  and  that  the  surface  of  the  earth  must  be  convex  instead  of 
flat.     Hence  the  earth  as  a  whole  must  be  a  globe  or  sphere. 

Changes  of  this  kind  are  easily  recognized  in  traveling  from  the 
northern  to  the  southern  border  of  the  United  States,  or  farther 
south  into  Mexico  or  Cuba.  They  may  be  verified  by  correspond- 
ence between  different  schools,  several  hundred  miles  apart  north 
and  south.  What  changes  would  be  noted  in  traveling  northward 
from  ^  to  ^  V 


Globular  Form  of  Earth  shown  by 
Visibility  of  Stars 


THE  EARTH  AS  A  GLOBE  21 

QUESTIONS 

Sec.  1.  What  are  the  chief  subjects  that  are  taught  in  Physical 
Geography  ? 

2.  What  is  the  view  generally  held  by  savage  races  as  to  the  size 
and  shape  of  the  earth  ?  When  were  correct  notions  first  gained  as 
to  the  earth's  shape  ?  llow  did  Aristotle  infer  the  earth's  shape  ? 
What  must  be  the  relative  positions  of  sun,  earth,  and  moon  when 
the  moon  is  eclipsed?    Why  is  the  moon  not  eclipsed  every  month? 

3.  When  was  the  earth's  size  first  determined?  When  and  by 
whom  was  the  earth  first  circumnavigated  ?  ,  Name  some  of  the 
places  then  discovered. 

4.  Describe  the  general  form  of  the  earth.  State  the  relation  of 
its  mountain  heights  and  ocean  depths  to  its  diameter.  Does  the 
earth's  form  favor  travel  and  transportation?     How? 

5.  How  are  savage  tribes  affected  by  the  size  of  the  earth  ?  In 
what  ways  have  civilized  nations  become  associated  with  one 
another  ? 

6.  What  is  meant  by  «  up  **  and  «  down  "  ?  How  is  the  surface 
of  a  quiet  body  of  water  related  to  the  direction  of  gravity  ?  How 
is  the  position  of  tree  trunks  and  house  walls  related  to  the  direction 
of  gravity?  What  consequences  of  the  action  of  gravity  are  seen  in 
men  and  animals? 

Ti  What  is  the  belief  of  primitive  man  about  the  ppsition  of  the 
earth  ?  What  are  the  facts  ?  What  is  the  effect  of  the  earth's  rotar 
tion  on  its  form  ? 

8.  What  is  the  cause  of  day  and  night?  What  is  the  most 
natural  unit  of  time  ?  What  habits  of  man  and  animals  result  from 
the  earth's  rotation?  How  are  the  cardinal  points  related  to  the 
earth's  rotation ?  What  is  the  position  of  the  sun  at  midday?  How 
are  midday  and  true  north  determined  ?  Given  a  north  and  south 
line,  how  can  you  determine  east  and  west? 

9.  Define  meridian  line,  meridian  circle,  poles,  parallels,  equator. 
What  is  latitude  and  how  is  it  measured  ?    What  is  meant  by  low, 


22  ELEMENTARY  PHYSICAL  GEOGRAPHY 

middle,  and  high  latitudes  ?    What  is  longitude  and  how  is  it  meas- 
ured ?     State  some  of  the  practical  uses  of  meridians  and  parallels. 

10.  Compare  the  sun*s  size  with  that  of  the  moon*s  orbit.  Calcu- 
late the  time  needed  for  an  express  train  to  reach  the  sun.  What  is 
the  earth's  orbit  ?  What  is  the  earth's  orbital  velocity?  How  is  it 
found  ?  What  are  the  stars  ?  What  can  be  said  of  their  distance 
from  us  ? 

11.  How  are  the  planets  distinguished  from  the  stars?  Which 
planets  can  be  seen  without  a  telescope  ?  Name  the  planets  in  order 
of  distance  from  the  sun.  Which  are  larger,  which  smaller,  than  the 
earth?  Compare  the  "day"  of  Jupiter  and  of  Saturn  with  our  day  ; 
the  «  year  "  of  Venus  and  of  Mercury  with  our  year.  State  the  size 
and  distance  of  the  moon. 

12.  What  is  the  solar  system?  What  features  are  possessed  in 
common  by  its  members  ?    What  do  these  common  features  suggest  ? 

13.  Of  what  is  the  great  body  of  the  earth  believed  to  consist? 
Why  ?*  What  is  meant  by  the  earth's  crust  ?  What  are  the  three 
states  of  matter?  Give  examples  of  them.  What  are  the  chief 
divisions  of  the  earth? 

14.  What  is  known  about  underground  temperatures?  At  what 
rate  does  temperature  increase  downward?  What  is  the  supposed 
condition  of  the  earth's  interior?  What  relation  is  suggested 
between  the-  earth's  surface  form  and  its  interior  temperature? 

15..  What  may  be  said  of  the  earth's  age  and  of  life  on  the 
earth? 

16.  How  is  a  small  balanced  magnet  affected  by  a  large  one? 
How  will  a  balanced  magnet  stand  when  alone?  What  is  a  com- 
pass ?  What  are  the  magnetic  poles  ?  Where  are  they  ?  How  far 
to  one  side  of  the  meridian  does  the  compass  point  at  your  school  ? 
Does  it  point  east  or  west  of  the  true  meridian  ? 

17.  Describe  the  aurora  boreaUs.  How  is  it  related  to  the  mag- 
netic pole  ? 


CHAPTER  II 
THE  ATMOSPHERE 

19.  The  Atmosphere  is  a  light  and  transparent  mixture 
of  gases,  known  as  air.  It  rests  upon  the  lands  and  seas, 
forming  the  outermost  part  of  the  earth.  It  takes  part  in 
the  earth's  daily  rotation  and  yearly  revolution. 

Many  processes  that  take  place  on  the  lands  and  seas 
depend  on  the  atmosphere.  The  waves  and  currents  of 
the  ocean  are  caused  by  the  winds  ;  the  soil  that  covers 
so  large  a  part  of  the  lands  results  from  the  decay  of  the 
underlying  rocks,  largely  through  the  action  of  moist  air. 
Rainfall,  so  important  in  many  ways,  is  supplied  by  mois- 
ture received  from  the  oceans  and  carried  about  by  the 
movements  of  the  atmosphere. 

The  atmosphere  far  overtops  the  highest  mountains. 
Meteors,  or  "falling  stars,"  —  small  scraps  of  matter  dash- 
ing toward  the  earth  from  outer  space  —  are  heated  by 
rushing  through  the  air  at  enormous  speed,  so  that  they 
become  luminous.  They  are  sometimes  seen  at  heights 
of  more  than  a  hundred  miles,  showing  that  some  air 
reaches  that  great  altitude. 

Cloud,  haze,  and  dust  make  the  lower  air  more  or  less 
turbid  and  often  shut  out  a  great  part  of  the  sun's  rays ; 
but  when  the  air  is  clear  it  is  so  transparent  that  sunlight 
is  strong  even  at  the  bottom  of  the  atmosphere. 


24  ELEMENTARY  PHYSICAL  GEOGRAPHY 

20.  Composition  of  Air.  —  Air  consists  of  a  uniform 
mixture  of  gases  in  which  a  small  and  variable  quantity 
of  water  vapor  is  usually  present.  The  chief  gases  are 
nitrogen  and  oxygen,  which  constitute  about  four  fifths 
and  one  fifth,  respectively,  of  the  atmosphere. 

Fire  is  the  result  of  an  active  combination  of  some  burn- 
able substance  with  the  oxygen  of  the  atmosphere.  The 
heat  thus  developed,  may  produce  light,  or  it  may  con- 
vert water  into  steam,  and  the  expansive  force,  of  the 
steam  may  be  used  to  drive  engines  and  many  kinds  of 
machinery. 

All  animals  and  plants  breathe  in' air  and  use  some  of 
its  oxygen  to  combine  with  part  of  their  substance  in  a 
very  slow  combustion,  which  produces  a  slight  amount  of 
heat,  but  no  fire.  Thus  all  forms  of  life,  animal  and  vege- 
table, depend  upon  the  oxygen  of  the  air,  as  well  as  upon 
their  food,  to  keep  them  alive. 

Carbonic  dioxide,  constituting  less  than  a  thousandth 
part  of  the  atmosphere,  is  nevertheless  important  for  the 
growth  of  plants.  The  carbon  taken  from  this  gas  by 
growing  plants  makes  a  large  part  of  their  structure. 

21.  Pressure  of  the  Atmosphere.  —  Although  the  air  is 
invisible,  it  is  attracted  by  the  earth  and  exerts  a  pressure 
of  about  a  ton  to  the  square  foot  upon  the  surface  on 
which  it  rests.  The  total  pressure  on  a  man's  body 
amounts  to  several  tons ;  but  this  is  not  felt  because  the 
air  within  the  body  exerts  a  corresponding  pressure  out- 
ward. The  air  is  so  easily  moved  that  little  resistance  is 
noticed  when  one  walks  through   it ;    but  fast  railroad 


THE  ATMOSPHERE 


26 


■i 


trains  are  much  impeded  by  the  resistance  of  the  air  that 
they  have  to  push  rapidly  aside. 

The  pressure  of  the  atmosphere  is  measured  by  the 
barometer.  This  instrument  is  of  two  kinds. 
The  mercurial  barometer,  Figure  8,  consists  of 
a  glass  tube,  somewhat  more  than  thirty  inches 
long  and  closed  at  one  end.  It  is  prepared  by 
filling  the  tube  with  mercury,  closing  the  open 
end  with  the  finger,  and  inverting  the  tube ; 
the  open  end  is  then  placed  in  a  vessel  of  mer- 
cury and  the  finger  is  withdrawn.  The  mer- 
cury sinks  a  little  below  the  closed  upper  end 
of  the  tube,  leaving  an  empty  space,  or  vacuum, 
above  it.  The  mercury  column  must  press 
down  on  part  of  the  mercury  in  the  vessel 
just  as  much  as  the  air  presses  on  any  equal 
part  of  the  mercury  surface.  Thus  the  height 
of  the  mercury  column,  measured  by  a  scale, 
may  be  taken  as  a  measure  of  the  pressure  of 
the  atmosphere. 

The  aneroid  barometer  consists  of  a  small 
box,  from  which  the  air  has  been  exhausted. 
A  variation  in  the  pressure  of  the  atmosphere 
causes  a  slight  change  in  the  shape  of  the 
box.  The  change  is  magnified  by  a  series  of 
delicate  levers,  by  which  an  index  is  moved 
on  a  dial.  The  reading  indicated  on  the  dial 
then  shows  the  pressure  of  the  atmosphere. 

The  ordinary  changes  of  atmospheric  pressure,  such  as 
may  be  seen  to  accompany  weather  changes  by  reading  a 


^1^ 


Fig.  8 
Mercurial 
Barometer 


26  ELEMENTARY  PHYSICAL  GEOGRAPHY 

barometer  from  hour  to  hour  and  from  day  to  day,  are 
seldom  more  than  a  thirtieth  or  a  fifteenth  of  the  total 
pressure. 

If  a  barometer  is  carried  up  a  lofty  mountain,  leaving 
much  of  the  atmosphere  beneath  it,  the  pressure  of  the 
overlying  atmosphere  is  found  to  be  much  reduced.  An 
ascent  of  a  thousand  feet  causes  a  lowering  of  about  an 
inch  in  the  barometric  column.  Thus  barometers  may  be 
used  to  measure  mountain  heights. 

Although  very  light,  the  air  supports  the  flight  of  birds 
and  insects.  The  wind  drives  sailing  vessels  and  wind- 
mills. In  dry  regions,  where  the  ground  is  not  covered 
with  vegetation,  the  shape  of  the  surface  is  changed  by  the 
long-continued  action  of  the  wind  in  drifting  sand  and 
dust  from  place  to  place. 

22.  Elasticity  of  the  Air.  —  Air  is  extremely  elastic, 
changing  its  volume  with  every  change  of  pressure.  Its 
lower  part  is  compressed  by  the  weight  of  the  overlying 
parts,  so  that  much  more  air  is  contained  in  a  cubic  foot 
at  sea  level  than  at  a  height  of  three  miles.  This  is 
expressed  by  saying  that  the  density  of  the  lower  air  is 
greater  than  that  of  the  upper  air.  A  cubic  foot  of  air  at 
sea  level  weighs  about  0.075  pound,  while  at  three  miles 
above  sea  level  its  weight  is  only  about  half  as  much,  and 
at  an  altitude  of  a  hundred  miles  the  air  must  be  almost 
imperceptible. 

Men  and  animals  living  on  high  plateaus  have  become 
accustomed  to  the  rarity  or  thinness  of  the  air  around 
them.     There  are  villages  on  the  plateau  of  Tibet  and  in 


THE  ATMOSPHERE  27 

the  higher  valleys  of  the  Andes  at  heights  of  from  12,000 
to  14,000  feet,  where  the  density  of  the  air  is  hardly  two 
thirds  of  that  at  sea  level.  Mountain  climbing  at  alti- 
tudes above  20,000  feet  is  almost  impossible,  from  the 
difficulty  of  breathing  the  thin  upper  air. 

It  is  by  slight  wavelike  movements  in  the  air  that 
sound  is  transmitted.  So  quickly  is  the  wavelike  dis- 
turbance passed  on  that  sound  travels  a  mile  in  five 
seconds.  So  easily  is  the  air  disturbed  that  a  locust 
(cicada)  may  set  hundreds  of  tons  of  air  vibrating  per- 
ceptibly to  our  nerves  of  hearing.  When  the  volcano 
Krakatoa,  between  Java  and  Sumatra,  exploded  in  August, 
1883,  sounds  were  heard  for  2000  miles,  and  atmospheric 
waves,  detected  by  slight  changes  of  pressure  in  barom- 
eters, passed  three  times  around  the  earth. 

23.  Colors  of  the  Atmosphere. — The  clear  atmosphere  is 
so  transparent  that  the  light  of  faint  stars  can  pass  through 
its  whole  thickness.  In  the  daytime  the  sun  lights  up 
the  sky  so  brightly  that  stars  are  not  seen.  The  blue 
color  of  the  clear  sky  is  due  to  the  scattering  of  sunlight 
on  countless  numbers  of  extremely  minute  particles,  the 
scattered  light  being  seen  against  the  darkness  of  outer 
space.  The  red  and  yellow  colors  near  the  horizon  at  sun- 
rise and^sunset  are  due  to  the  sifting  out  of  other  colors  as 
the  sunlight  passes  obliquely  through  a  great  thickness  of 
atmosphere. 

As  the  sun  sinks  slowly  below  the  western  horizon 
after  a  clear  sunset,  a  pink  or  rosy  arch  of  sunlit  air  — 
the  twilight  arch  —  may  be  seen  slowly  rising  over  the 


28  ELEMENTARY  PHYSICAL  GEOGRAPHY 

eastern  horizon ;  the  dull  blue  sky  below  the  arch  is  dark- 
ened by  the  shadow  of  the  earth.  A  similar  arch  and 
shadow  may  be  seen  sinking  in  the  west  before  a  clear 
sunrise.  Thus  the  shadow  of  night  may  be  seen  follow- 
ing the  sunlit  air  of  one  day  and  disappearing  before  the 
sunlight  of  the  next. 

24.  Temperature  of  the  Atmosphere.  —  The  temperature 
of  the  land  and  sea  surface  and  of  the  atmosphere  is  con- 
trolled by  the  rays  of  the  sun.  The  temperature  of  the 
atmosphere  is  not  much  affected  directly  by  the  sun's  rays, 
because  the  air  is  so  transparent  that  the  rays  are  very  little 
taken  in  or  absorbed  by  it;  hence  the  upper  air  is  every- 
where cold.  The  temperature  -of  the  lower  air  is  largely 
controlled  by  the  temperature  of  the  land  or  sea  surface  on 
which  the  air  rests.  The  sea  surface  absorbs  the  sun's  rays 
somewhat  more  actively,  and  the  land  surface  much  more 
actively,  than  the  air  does ;  thus  they  become  warmer  than 
the  air.  The  air  lying  next  to  the  heated  surface  is  then 
warmed  by  heat  that  is  carried  or  conducted  from  the  land 
or  sea  to  the  air. 

At  night,  when  sunshine  is  absent,  land,  sea,  and  air  cool 
by  radiating  their  own  heat  (giving  out  rays)  toward  outer 
space.  Just  as  the  air  absorbs  the  rays  of  the  sun  very  imper- 
fectly in  the  daytime,  so  it  gives  up  very  little  of  its  own 
heat  by  radiating  at  night.  The  sea  surface  is  somewhat 
more  active  than  the  air  in  cooling  by  radiation  at  night, 
and  the  land  surface  is  much  more  so.  Hence  the  lower  air 
is  cooled  at  night  by  conduction  of  its  heat  to  the  cooling 
surfaces  on  which  it  rests.     In  the  upper  air  the  diurnal 


THE  ATMOSPHERE  29 

range  or  the  change  of  temperature  from  day  to  night  is 
very  small ;  it  is  somewhat  greater  in  the  lower  air  on  the 
oceans ;  it  is  much  greater  in  the  lower  air  on.  the  lands. 

The  sun's  rays  fall  almost  vertically  on  every  part  of  the 
earth's  surface  near  the  equator  for  several  midday  hours, 
and  there  high  temperatures  must  prevail.  The  rays  fall 
obliquely  on  the  polar  regions,  so  that  each  ray  is  there 
spread  over  a  larger  surface  than  in  the  torrid  zone,  and 
its  noon  effect  is  no  greater  than  that  of  an  early  morning 
or  afternoon  ray  near  the  equator ;  hence  low  temperatures 
must  prevail  around  the  poles.  This  may  be  illustrated 
by  the  difference  in  the  heating  effect  of  sunshine  on  the 
two  slopes  of  a  road  that  runs  north  and  south  over  a  hill. 
Between  poles  and  equato*  intermediate  temperatures  are 
maintained. 

High,  medium,  and  low  temperatures  are  thus  distrib- 
uted in  belts  —  hot,  medium,  and  cold  —  roughly  parallel 
to  the  equator;  the  belts  are  known  as  the  torrid,  tem- 
perate, and  frigid  zones.  Fortunately  the  cold  or  frigid 
areas  occupy  a  relatively  small  part  of  the  world. 

Yet  even  in  the  torrid  zone  lofty  mountains  rise  into 
air  that  is  so  cold  that  snow  lies  on  their  upper  parts  all 
the  year  round.  The  lower  limit  of  the  permanent  snow 
fields  is  called  the  snow  line.  It  is  about  three  miles 
above  sea  level  in  the  mid-torrid  zone;  about  a  mile  above 
in  latitude  55°  or  60°  N.  or  S.;  it  descends  to  sea  level 
within  the  frigid  zone,  where  permanent  snow  may  be 
found  even  on  the  lowlands. 

Heated  air  expands.  Hence,  volume  for  volume,  hot 
air  is  lighter  than  cold  air;  the  air  of  the  torrid  zone  is 


30  ELEMENTARY  PHYSICAL  GEOGRAPHY 

lighter  than  that  of  the  frigid  zones.     This  fact  will  be 
found  of  great  importance  as  a  cause  of  the  winds. 

25.  Mirage.  —  A  curious  consequence  of  the  strong 
control  of  air  temperature  by  that  of  the  land  or  sea  sur- 
face on  which  the  air  rests  is  sometimes  seen  in  the  reflec- 
tion of  distant  objects  by  the  lower  layer  of  air  when  its 
temperature  is  distinctly  unlike  that  of  the  overlying  air. 
A  reflection  of  this  kind  is  called  a  mirage  (Frencb,  mean- 
ing "reflection";  pron.  meerahzh).     Its  cause  is  as  follows: 


Fig.  9.     Mirage  of  Part  of  a  Schooner,  formed  on  a  Thin  Layer  of  Air 

The  surface  of  a  level  desert  in  a  warm  zone  becomes 
very  hot  under  unclouded  summer  sunshine,  and  the  air 
close  to  the  ground  is  heated  by  conduction,  so  that  it 
becomes  much  hotter  than  that  three  or  four  feet  higher. 
The  upper  surface  of  the  hot  air  acts  like  a  mirror  and 
gives  an  inverted  reflection  of  objects  beyond  it.  The 
reflecting  air  surface  thus  imitates  a  water  surface  so  well 
that'  travelers  are  often  deceived  by  it  and  think  that  a 
lake  exists  where  in  reality  there  is  nothing  but  dry 
sand. 


THE  ATMOSPHERE  31 

When  cold  air  blows  over  a  warmer  sea  its  lower  layer 
may  be  heated  by  conduction  from  the  water,  so  as  to 
become  distinctly  warmer  than  the  air  at  a  greater  height. 
When  warm  air  blows  over  a  colder  sea  the  lower  part 
may  be  cooled  by  conduction.  In  either  case  the  lower 
layer  may  reflect  the  figure  of  distant  vessels,  the  reflected 
image  being  seen  upside  down  beneath  the  object  itself,  if 
the  lower  layer  of  air  is  thin  and  the  observer  is  above  it ; 
but  above  the  object  itself,  if  the  lower  layer  is  thicker 
and  the  observer  is  within  it. 

The  equivalent  of  a  mirage  may  often  be  seen  by  look- 
ing close  along  a  brick  wall  that  is  exposed  to  strong  sun- 
shine in  calm  warm  weather.  Objects  that  are  nearly  in 
line  with  the  wall  may  be  seen  reflected  on  the  film  of  hot 
air  next  to  it. 

26.  Thermomefers.  —  The  temperature  of  the  air  and 
of  other  bodies  may  be  measured  by  the  thermometer 
(temperature  measure),  consisting  of  a  fine  tube  opening 
into  a  bulb  at  its  lower  end  and  containing  mercury  (or 
other  liquid).  The  glass  and  the  mercury  take  the  tem- 
perature of  the  surrounding  air.  If  warmed,  both  expand, 
but  the  liquid  mercury  expands  more  than  the  solid  glass, 
and  part  of  the  mercury  is  therefore  pushed  from  the  bulb 
into  the  tube ;  if  cooled,  both  contract  and  some  of  the 
mercury  is  withdrawn  from  the  tube  into  the  bulb.  Thus 
the  height  of  the  mercury  in  the  tube  measures  relative 
heat  and  cold,  or  temperature. 

In  the.  United  States  and  Great  Britain  it  is  still 
customary  to  employ  the   Fahrenheit  thermometer  (F.), 


32 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


marking  32°  at  the  freezing  point  and  212°  at  the  boiling 
point  of  water.  In  continental  Europe  the  Centigrade 
thermometer  (C.)  is  used,  reading  0°  at  the  freezing  and 
100°  at  the  boiling  point. 

Some  thermometers  are  arranged  so  as  to  give  a  contin- 
uous temperature  record  in  a  curve  drawn  on  a  sheet  of 
paper;  such  instruments  are  called  self-recording  ther- 
mometers, or  thermographs, 
one  pattern  being  shown  in 
Figure  10.  Others  are  con- 
trived so  as  to  register  the 
highest  (maximum)  and  low- 
est (minimum)  temperatures 
of  the  day;  this  is  sometimes 
done  by  placing  an  index  or 
short  piece  of  fine  wire  inside 
the  tube,  so  that  it  may  be 
pushed  up  or  down  as  the 
liquid  expands  or  contracts. 
Such  instruments  are  called 
maximum  and  minimum  ther- 
mometers. 

When  the  thermometer  is  used  to  measure  the  tempera- 
ture of  the  air  it  should  be  suspended  so  as  to  be  protected 
from  direct  sunshine  and  from  rain  and  snow,  but  exposed 
to  the  wind.  If  placed  outside  of  a  window,  the  thermom- 
eter should  be  on  the  north  side  of  the  building,  free  from 
the  wall  and  where  warm  air  escaping  from  windows 
cannot  affect  it.  It  is  better  placed  in  a  special  shelter, 
away  from  buildings  and  trees. 


Fig.  10 

The  Comey  Self-Recording 

Thermometer 


THE  ATMOSPHERE 


33 


27.  Temperature  Charts  and  Mean  Temperatures.  —  The 
distribution  of  temperature  is  indicated  on  charts  by  lines 
drawn  through  places  having  the  same  temperature. 

Figure  11  gives  the  degrees  of  temperature  prevailing 
over  the  middle  and  eastern  United  States  on  a  certain 
morning.  The  dotted  line  is  drawn  so  as  to  separate 
all  places  having 
higher  temperatures 
(warmer)  than  40° 
from  those  having 
lower  temperatures 
(colder).  Similar 
lines  may  be  drawn 
for  temperatures 
of  10°,  20°,  30°, 
50°,  and  60°.  Each 
of  these  lines  is 
called  an  isother- 
mal (equal  tem- 
perature) line,  or 
isotherm.  It  is  a 
line  of  uniform  temperature,  separating  regions  of  higher 
and  lower  temperature. 

In  the  example  here  given  all  the  states  northwest 
of  a  line  drawn  from  the  southwest  corner  of  Arkan- 
sas to  the  western  end  of  Lake  Erie  have  temperatures 
lower  than  40°.  All  the  states  southeast  of  this  line 
have  temperatures  higher  than  40°.  Many  illustrations 
of  this  kind  are  afforded  by  the  daily  weather  maps 
issued  by  the  national  Weather  Bureau.     What  would  be 


Fig.  11.    Illustration  of  an  Isothermal  Line 


34 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


the  temperature  of  a  place  halfway  between  the  isotherms 
of  50°  and  60°? 

If  records  of  temperature  are  kept  at  regular  hours 
every  day  for  a  month,  the  hours  being  chosen  so  as  to 
include  the  cooler  as  well  as  the  warmer  periods  of  the 
day,  the  sum  of  all  the  temperatures  divided  by  the 
number  of  observations  will  give  the  average  or  mean 


Fig.  12.    Chart  of  Mean  Annual  Temperatures 

temperature  of  the  month.  Similarly,  if  observations  are 
kept  up  through  a  whole  year,  the  mean  temperature  of 
the  year  may  be  determined.  The  mean  temperatures 
of  a  place  for  a  year  usually  differ  by  a  small  amount  in 
successive  years ;  hence  the  standard  mean  annual  tempera- 
ture of  a  place  is  determined  by  averaging  the  means  of 
ten  or  twenty  successive  years.  Observations  of  temper- 
ature have  now  been  made  during  many  years  at  a  great 


THE  ATMOSPHERE  35 

many  places,  so  that  the  distribution  of  temperature  all 
over  the  world,  except  in  the  two  frigid  zones,  is  fairly 
well  known. 

The  distribution  of  mean  annual  temperatures  for  the 
year  is  shown  by  isotherms  on  the  chart  of  the  world, 
Figure  12,  which  is  therefore  called  a  chart  of  annual  iso- 
therms. A  line  drawn  near  the  earth's  equator,  through 
the  middle  of  the  belt  of  greatest  heat,  is  called  the  heat 
equator,  the  average  temperature  of  which  is  about  80°. 
From  the  heat  equator  the  temperature  decreases  toward 
each  pole  at  the  rate  of  about  one  degree  of  the  Fahrenheit 
thermometer  scale  to  a  degree  of  latitude. 

In  the  southern  hemisphere  the  isotherms  are  nearly 
parallel  to  the  latitude  circles ;  this  is  because  the  oceans 
there  are  so  little  interrupted  by  land. 

In  the  northern  hemisphere  the  isotherms  are  much 
more  irregular,  because  the  oceans  are  here  interrupted 
by  broad  continents,  and  the  temperatures  on  lands  and 
seas  are  often  unlike  in  the  same  latitude. 

Exercise.  What  parts  of  the  lands  and  oceans  have  a  mean 
annual  temperature  above  70°?  above  80°?  What  is  the  general 
path  of  the  isotherm  of  zero  in  the  northern  hemisphere  ?  Estimate 
from  the  chart  the  mean  annual  temperature  of  your  home ;  of  Lon- 
don; of  Cape  of  Good  Hope. 

28.    Circulation  of  the  Atmosphere Movements  of  the 

atmosphere  are  usually  caused  by  differences  of  tempera- 
ture. For  example,  a  movement  of  air  will  take  place 
between  two  rooms,  one  warm  and  the  other  cold,  if  a  door 
is  opened  between  them.  The  cold  air  is  heavier  than  the 
warm  air.     Cold  air  will  therefore  creep  into  the  lower 


36      ELEMENTARY  PHYSICAL  GEOGRAPHY 

part  of  the  warm  room,  while  the  light  warm  air  spreads 
into  the  upper  part  of  the  cold  room.  The  movement  may 
be  shown  by  the  drift  of  smoke  from  a  smoldering  match. 
If  the  cold  air  is  warmed  as  it  enters  the  warm  room,  and 
the  warm  air  is  cooled  as  it  enters  the  cold  room,  the 
movement  will  continue  indefinitely,  the  air  going  round 
and  round  in  a  circuit.  Such  a  movement  is  called  a 
circulation.  It  is  also  called  a  convectional  circulation, 
because  heat  and  cold  are  conveyed  by  the  movement  that 
is  excited  by  differences  of  temperature. 

In  the  same  way  the  cold  air  of  the  polar  regions,  being 
heavier  than  the  warm  air  of  the  torrid  zone,  continually 
tends  to  creep  under  it,  thus  forming  convectional  air  cur- 
rents in  the  lower  atmosphere,  which  we  know  as  winds. 
The  warm  air,  being  slowly  raised  all  around  the  equatorial 
belt,  tends  to  overflow  north  and  south  toward  the  poles, 
forming  convectional  air  currents  at  a  great  height  in  the 
atmosphere. 

The  lower  winds  approaching  the  equator  where  sun- 
shine is  strong  are  warmed;  thus  their  air  is  expanded 
and  made  lighter,  so  that  it  is  in  turn  slowly  raised  over 
the  equatorial  belt  to  form  the  overflow  toward  the  poles. 
The  upper  currents,  flowing  toward  the  poles,  where  sun- 
shine is  weak,  are  slowly  cooled;  hence  their  air  settles 
down  to  lower  levels  and  forms  the  currents  returning 
toward  the  equator.  A  permanent  interchanging  move- 
ment or  circulation  is  thus  established  between  the  warmer 
and  colder  parts  of  the  earth.  It  must  continue  as  long  as 
the  sun  warms  the  equatorial  more  than  the  polar  regions. 
On  account  of  the  earth's  rotation  the  air  does  not  move 


THE  ATMOSPHERE  87 

directly  north  and  south,  but  is  turned  obliquely  toward 
the  east  or  west.     (See  page  85.) 

Changes  of  temperature  in  the  circulating  atmosphere  are 
produced  not  only  during  movements  toward  or  from  the 
equatorial  belt,  but  also  during  the  ascent  or  descent  of  the 
air  currents.  As  the  warm  air  rises  the  pressure  of  the  over- 
lying atmosphere  upon  it  is  less  and  less;  the  rising  air 
therefore  expands,  and  in  so  doing  it  is  cooled ;  hence  even 
over  the  torrid  zone  the  upper  atmosphere  is  cold*.  On  the 
other  hand,  as  the  descending  air  in  higher  latitudes  sinks 
to  lower  levels  a  greater  and  greater  amount  of  air  rests 
upon  it ;  it  is  thus  compressed  and  warmed.  The  descent 
of  air  from  a  great  altitude  is  therefore  not  a  cause  of  cold, 
for  the  air  is  warmed  by  compression  as  it  comes  down. 

Changes  of  temperature  of  this  kind  will  later  be  seen 
to  be  of  importance  in  producing  and  in  dissolving  rain 
clouds.  Illustrations  of  such  changes  may  be  found  in  a 
small  way  by  noting  the  coolness  of  the  air  that  expands  as 
it  flows  out  of  a  bicycle  tire  when  the  valve  is  opened,  and 
the  warmth  of  an  air  pump  in  which  air  has  been  com- 
pressed in  order  to  force  it  into  a  tire. 

The  most  general  movements  of  the  atmosphere  thus 
established  on  a  planet  like  the  earth  may  be  called  the 
planetary  circulation ;  the  lower  members  of  this  circula- 
tion are  the  planetary  winds.  The  surface  winds  move 
much  slower  than  the  upper  currents,  on  account  of  fric- 
tion with  the  earth's  surface. 

29.    Observation  of  Winds The  direction  of  the  wind 

is  determined  by  a  vane   or  arrow,  turning  easily  on  a 


38 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


vertical  axis  and  freely  exposed,  as  on  a  spire  or  high  pole, 
to  the  movement  of  the  air.  The  wind  is  named  after  the 
point  of  the  compass  from  which  it  blows. 

The  strength  of  the  wind  may  be  described  as  light,  mod- 
erate, strong  (twenty  miles  an  hour),  fresh  gale,  whole  gale, 
hurricane  (seventy-five  or  more  miles  an  hour) ;  or  it  may  be 

determined  in  miles 
per  hour  by  an  anemo- 
meter (wind  measure) 
turning  on  a  vertical 
axis,  as  in  Figure  13. 

Describe  the  arrange- 
ment of  the  cups  on  the 
arms  of  this  instrument. 
Which  way  will  the  arms  turn 
when  the  wind  blows  ?     Why  ? 

A  pointer  on  a  small  dial, 
connected  with  the  axis  of 
the  turning  arms  by  cog- 
wheels, indicates  the  move- 
ment of  the  wind  in  miles 
per  hour. 
The  surface  wind  on  the  uneven  lands  seldom  blows  in 
straight  lines  with  uniform  velocity.     It  usually  rolls  and 
whirls,  now  faster,  now  slower. 


Fig.  13.    Anemometer 


30.  Rainfall.  —  Water  is  evaporated  from  the  ocean 
surface,  especially  from  its  warmer  parts,  and  the  invisible 
vapor  thus  formed  mixes  with  the  air  and  is  carried  about 
in  the  winds.     When  the  moist  air  is  sufficiently  cooled 


THE  ATMOSPHERE  39 

the  vapor  in  it  is  condensed  into  minute  water  drops  or 
snow  crystals,  and  the  air  becomes  cloudy.  If  the  cooling 
continues  still  further,  rain  or  snow  may  fall.  The  vapor 
may  thus  be  returned  directly  to  the  oceans,  or  it  may  fall 
upon  the  lands,  whence  it  returns  to  the  oceans  in  streams 
and  rivers.  In  this  way  there  is  a  circulation  of  water 
through  the  atmosphere,  from  the  ocean  and  back  again. 

The  processes  by  which  the  air  is  cooled  are  nearly 
always  connected  with  its  movements.  Hence  the  general 
distribution  of  rainfall  will  be  referred  to  in  the  following 
account  of  the  winds,  while  a  fuller  account  of  clouds,  rain, 
and  snow  will  be  given  farther  on. 

31.  Planetary  Winds. — The  most  important  members 
of  the  planetary  winds  are  the  trade  winds  and  the  pre- 
vailing westerlies. 

The  trade  winds  blow  with  much  regularity  from  about 
latitude  28°  N.  and  S.  obliquely  toward  a  belt  of  low  atmos- 
pheric pressure  around  the  equator,  from  the  northeast 
in  the  northern  hemisphere,  and  from  the  southeast  in 
the  southern.  The  prevailing  westerly  winds  blow  from 
a  westerly  source,  but  usually  with  a  slight  inclination 
toward  the  pole,  over  the  greater  part  of  the  temperate 
zones ;  they  form  great  spiral  whirls  around  regions  of  low 
pressure  in  the  high  latitudes  of  each  hemisphere.  These 
winds  are  made  irregular  by  the  occurrence  of  many 
smaller  whirls,  about  1000  miles  in  diameter,  which  drift 
eastward  with  the  general  movement  of  the  atmosphere 
in  middle  latitudes.  The  winds  of  the  polar  regions  are 
little  known. 


40 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Karrow  belts  of  light  variable  winds  and  frequent  calms 
lie  between  the  several  belts  of  steadier  winds;  in  these 
belts  of  light  winds  the  pressure  of  the  atmosphere  is  so 
nearly  uniform  that  the  air  is  not  pushed  steadily  in  any 

direction.  All  these  mem- 
bers of  the  planetary  circu- 
lation are  better  defined  over 
the  oceans  than  on  the  lands. 

r":-  Point  out  and  name  the  several 


'  Ym  'members  of  the  planetary  circula- 
tion in  Figure  14.  In  what 
directions  do  their  winds  blow? 
Between  what  latitudes  do  they 
occur? 


Fig.  14.    The  Planetary  Circulation 
of  the  Atmosphere 


The  trade  winds  are  so 
called  from  the  constancy 
with  which  they  follow  their 
course,  the  word  trade  formerly  having  meant  "steady." 
They  warm  slowly  as  they  approach  the  heat  equator. 
Their  velocity  at  sea  is  from  ten  to  thirty  miles  an  hour. 
They  give  fair  weather,  seldom  interrupted  by  storms. 

When  sailing  vessels  enter  the  trade-wind  belt  they  may 
count  upon  making  good  headway.  If  sailing  with  the 
winds,  extra  sails  are  often  rigged  out  on  the  ends  of  the 
yards,  and  thus  aided  by  a  broadened  stretch  of  canvas 
the  vessels  speed  along  day  and  night. 

Coasts  upon  which  the  trade  winds  blow  are  usually, 
beaten  with  heavy  surf,  so  that  landing  is  difficult,  except 
in  well-protected  harbors.  This  is  the  case  on  the  north- 
east side  of  the  Windward  islands  in  the  Lesser  Antilles. 


THE  ATMOSPHERE  41 

Lowlands  over  which  the  trade  winds  blow  are  made 
desert  by  the  drying  action  of  their  warming  air;  for  as 
the  winds  become  warmer  they  take  up  any  moisture  that 
they  find  instead  of  giving  up  what  they  have.  The  Afri- 
can Saliara  and  the  central  Australian  deserts  are  thus 
explained :  it  is  entirely  on  account  of  their  dryness  and 
not  because  of  the  infertility  of  their  soils  that  these 
regions  are  barren. 

Where  the  trade  winds  encounter  mountain  ranges  they 
are  forced  to  ascend  tlie  side  on  which  they  approach  (the 
windward  side).  As  they  rise  the  air  expands  and  cools; 
as  the  air  cools  some  of  the  invisible  vapor  that  it  contains 
is  condensed  into  minute  drops  of  water ;  thus  the  ascend- 
ing air  becomes  cloudy  and  rainy.  The  eastern  slope  of 
the  Andes,  about  the  headwaters  of  the  Amazon,  the 
mountains  along  the  east  coast  of  Brazil  under  the  south- 
east trades,  and  the  eastern  slopes  of  the  highlands  of 
Mexico  and  Central  America  under  the  northeast  trades 
thus  receive  a  good  amount  of  rainfall  (80  to  100  inches  a 
year).     All  these  mountain  slopes  bear  heavy  forests. 

The  further  slope  of  the  mountains,  where  the  winds 
descend  (the  leeward  side),  is  relatively  dry  and  barren, 
because  as  the  air  descends  it  is  compressed  by  the  weight 
of  the  air  that  follows  upon  it;  as  it  is  compressed  it  is 
warmed,  and  as  it  warms  it  holds  all  the  vapor  that  it  has 
and  eagerly  takes  up  any  vapor  it  can  get  from  the  ground 
over  which  it  blows.  This  is  especially  noticeable  on  the 
western  side  of  the  Peruvian  Andes,  where  much  of  the 
land  is  a  desert  in  spite  of  being  near  the  ocean. 

Even  in  the  Sahara  the  few  mountains  that  interrupt 


42 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


the  general  surface  receive  a  sufficient  rainfall  to  permit 
tree  growth ;  but  the  streams  supplied  on  the  mountain 
sides  wither  away  after  descending  to  the  desert  below. 

The  prevailing  westerlies  are  much  less  regular  than  the 
trades.  They  may  weaken  to  less  than  ten  miles  an  hour, 
or  strengthen  to  gales  of  sixty  or  more  miles  an  hour. 

They    often    shift 


100  MILES 


from  their  general 
course  to  take  part 
in  the  drifting  spiral 
movements  indicated 
in  the  temperate  lati- 
tudes of  Figure  14. 
It  is  chiefly  to  these 
great  whirllike 
movements  that  the 
frequent  changes  of 
weather  in  temper- 
ate latitudes  are  due. 
The  area  of  the 
United  States  lies 
almost  entirely 
within  the  belt  of  the  prevailing  westerlies.  If  the  wind  is 
observed  at  noon  eveiy  day  for  a  month  or  two,  a  westerly 
direction  will  be  found  more  common  than  an  easterly.  If 
the  drift  of  clouds  is  observed,  the  general  movement  of 
the  atmospheric  currents  from  the  western  toward  the 
eastern  side  of  the  sky  is  very  noticeable.  Variations  from 
these  prevalent  directions  are  generally  due  to  the  drifting 
spiral  movements. 


Fig.  15.  Wet- Weather  Streams  of  the  Tarso 
Mountains,  Sahara.  Locate  these  mountains 
on  the  chart  of  mean  annual  temperatures, 
Figure  12,  by  the  latitude  and  longitude  here 
given 


THE  ATMOSPHERE  43 

The  lands  under  the  westerly  winds  are  generally  well 
watered  if  they  do  not  lie  too  far  from  the  oceans  ;  the  con- 
tinental interiors  are  comparatively  dry.  Abundant  rain- 
fall is  received  on  the  mountainous  Pacific  slopes  of  North 
and  South  America  in  middle  latitudes,  but  the  opposite 
slopes  are  drier.  In  these  latitudes  the  western  (wind- 
ward) slope  of  the  mountains  is  heavily  forested,  while  the 
eastern  (leeward)  slope  hiis  an  open  tree  growth  or  none. 
The  distribution  of  forests  over  the  great  American  moun- 
tain system  thus  gives  striking  illustration  of  the  relation 
of  timber  supply  to  winds,  land  forms,  and  rainfall. 

The  belt  of  calms  and  light  breezes  in  the  neighborhood 
of  the  equator,  between  the  trade  winds,  is  called  the 
equatorial  calm  belt ;  that  part  of  the  belt  which  lies  on 
the  oceans  is  known  to  sailors  as  the  doldrums.  The  air 
in  the  doldrums  is  moist  and  sultryf  for  the  warm  inflow- 
ing trade  winds  gather  much  water  vapor  as  they  blow 
over  the  ocean.  The  sky  is  prevailingly  cloudy;  rain 
falls  every  day  or  two,  especially  in  the  late  afternoon  or 
night  The  lands  are  heavily  forested  under  this  warm 
and  moist  belt,  and  agriculture  is  difficult  from  the  very 
luxuriance  of  vegetation. 

Sailing  vessels  bound  across  the  equator  are  frequently 
becalmed  for  several  days  in  the  doldrums ;  there  they  lie 
idle,  rocking  very  gently  to  and  fro  in  the  long  flat  swell 
that  sweeps  across  the  glassy  waters.  They  must  then 
take  advantage  of  every  light  breeze  to  push  onward  and 
reach  the  trade  winds  beyond.  The  dull  sky,  the  sultry 
air,  and  the  glassy  sea  make  the  delay  all  the  more 
vexatious. 


44  ELEMENTARY  PHYSICAL  GEOGRAPHY 

The  rain  of  the  doldrums  results  from  the  slow  ascent  of 
the  warm  moist  air  supplied  by  the  inflowing  trade  winds. 
The  lower  air  is  raised  to  greater  and  greater  height  by  the 
inflow  of  more  air  beneath  from  both  sides ;  it  expands  as 
it  rises,  and  cools  as  it  expands;  the  vapor  in  the  air  is 
then  condensed  into  cloud  particles,  the  clouds  become 
heavier  and  heavier  and  give  forth  plentiful  rain ;  the  air 
from  which  the  rain  has  fallen  continues  to  rise  and  at 
last  overflows  aloft  and  thus  supplies  the  upper  currents 
that  move  obliquely  toward  the  poles.  Violent  thunder- 
storms are  frequently  formed  in  the  great  cloud  masses  of 
the  calm  belt. 

The  ill-defined  belts  of  light  breezes  and  occasional 
calms  lying  between  the  trades  and  the  prevailing  wester- 
lies in  each  hemisphere  are  known  as  the  horse  latitudes. 
Their  light  winds  usife,lly  blow  obliquely  outward  on  both 
sides ;  hence  the  air  here  must  slowly  descend  from  the 
upper  currents  to  supply  the  outflowing  breezes.  As  the 
air  slowly  settles  down  it  is  compressed  by  the  weight  of 
that  which  rolls  in  on  top  of  it ;  as  it  is  compressed  it  is 
warmed,  and  as  it  is  warmed  any  clouds  that  it  may  have 
contained  are*dissolved;  hence  clear  fair  weather  is  preva- 
lent in  this  belt. 

32.  Whirls  of  the  Westerly  Winds.  —  The  irregular 
winds  by  which  the  prevailing  westerlies  are  so  often 
interrupted  sometimes  have  an  inward,  sometimes  an  out- 
ward, spiraling  movement,  as  in  Figure  16.  They  are  like 
great  slow-turning  whirls  from  500  to  1000  miles  in  diame- 
ter ;  they  may  be  compared  to  eddies  in  streams  of  water. 


THE  ATMOSPHERE 


45 


When  blowing  outward  the  air  slowly  descends  from 
aloft ;  the  winds  are  light  and  the  weather  is  fair,  for  the 
reasons  already  given  for  the  fair  weather  of  the  horse 
latitudes.  When  blowing  inward  the  air  slowly  ascends, 
and  the  weather  is  cloudy  and  wet,  for  the  reasons  given  in 
explaining  the  doldrums.  Here  the  winds  may  gain  a 
stormy  strength,  fifty  to  eighty  miles  an  hour  on  land  and 
sometimes  over  one  hun- 
dred miles  an  hour  at  sea. 


Exercise.  Locate  the  cen- 
ters of  the  two  whirls  shown 
in  Figure  16.  Describe  the 
spiral  movement  of  the  winds 
with  respect  to  the  centers. 
In  which  whirl  does  the  turn- 
ing around  the  center  agree 
with  the  turning  of  the  hands 
of  the  clock?  Which  whirl 
should    have    low    pressure? 

Which  one  fair  weather?  ^      ..,     ,         ,      ,  ^  ,  ,„  .  , 

Fig.  10.    Inward  and  Outward  Whirls 

Both  classes  of  whirls 
travel  from  500  to  1000  miles  a  day  in  an  easterly  direc- 
tion, with  the  general  drift  of  the  atmosphere'in  temperate 
latitudes.  Changes  of  weather  are  caused  by  their  pas- 
sage. The  whirls  may  strengthen  and  increase  in  area  for 
a  time,  then  weaken  and  fade  away ;  their  duration  being 
from  a  few  days  to  two  or  three  weeks,  and  their  distance 
of  travel  from  5000  to  15,000  miles  or  more.  The  direc- 
tion in  which  the  whirls  turn  in  the  northern  hemisphere 
is  opposite  to  that  in  the  southern ;  that  is,  the  outflowing 
spirals  turn  clockwise  in  the  northern  hemisphere,  as  in 


46  ELEMENTARY  PHYSICAL  GEOGRAPHY 

Figure  16,  and  counter-clockwise  in  the  southern  hemi- 
sphere. How  do  the  inflowing  spirals  turn  in  the  two 
hemispheres  ? 

The  pressure  of  the  atmosphere,  as  shown  by  the  barom- 
eter, is  less  than  usual  about  the  central  part  of  the  stormy- 
inward  whirls,  and  greater  than  usual  in  the  fair-weather 
outward  whirls.  Hence  they  are  often  called  low-pressure 
and  high-pressure  areas.  They  have  also  been  named 
cyclonic  and  anticyclonic  areas  from  the  curving  move- 
ment of  their  winds.  They  will  be  further  described  in 
the  section  on  weather. 

33.  Seasons  and  Zones.  —  As  the  earth  moves  around 
the  sun  there  are  six  months  in  each  year  (March  21 
to  September  22)  in  which  the  northern  hemisphere  is 
inclined  somewhat  toward  the  sun,  so  that  it  has  longer 
days  and  stronger  sunshine  than  the  southern,  which  is  at 
the  same  time  inclined  somewhat  away  from  the  sun,  as  in 
Figure  17. 

In  this  condition  the  gain  of  heat  in  the  northern  hemi- 
sphere by  the  absorption  of  the  strong  sunshine  during  the 
long  days  is  greater  than  the  loss  of  heat  by  radiation  dur- 
ing the  short  nights ;  hence  the  temperature  there  rises 
above  the  mean  of  the  year.  But  in  the  southern  hemi- 
sphere the  loss  of  heat  by  radiation  during  the  long 
nights  is  greater  than  the  gain  by  absorption  of  weak  sun- 
shine during  the  short  days ;  hence  the  temperature  there 
falls  below  the  mean  of  the  year.  During  these  months 
the  northern  may  be  called  the  summer  hemisphere,  and 
the  southern  the  winter  hemisphere. 


THE  ATMOSPHERE 


47 


During  the  other  six  months  of  the  year  (September  22 
to  March  21)  the  southern  hemisphere  is  inclined  toward 
the  sun,  and  the  northern  away  from  it,  so  that  the  above 


N  « 


Fig.  17.    Monthly  Positions  of  the  Earth  with  Respect  to  the  Sun 


conditions  are  reversed.     The  southern  is  then  the  sum- 
mer hemisphere,  and  the  northern  the  winter  hemisphere. 
In  both  hemispheres  the  succession  of  higher  and  lower 
temperatures    during   the   year   produces   the   change  of 


48  ELEMENTARY  PHYSICAL  GEOGRAPHY 

seasons.  The  winter  months  in  the  northern  hemisphere 
are  December,  January,  and  February  (these  being  the 
summer  months  of  the  southern  hemisphere) ;  the  spring 
months  are  March,  April,  and  May ;  the  summer  months, 
June,  July,  and  August;  the  autumn  or  fall  months, 
September,  October,  and  November. 

The  zones  may  be  defined  by  means  of  Figure  17  as  fol- 
lows :  In  the  torrid  zone,  from  231°  N.  to  231-°  S.,  every 
point  receives  vertical  sunshine  sometime  in  the  year; 
here  the  days  do  not  vary  much  from  twelve  hours  in 
length.  In  the  frigid  zone,  extending  23^°  from  each 
pole,  there  is  at  least  one  day  in  the  year  when  the  sun 
does  not  rise  and  another  when  it  does  not  set ;  here  the 
days  vary  greatly  in  length.  The  temperate  zones  occupy 
the  space  between  the  torrid  and  the  frigid  zones  (231° 
to  QQ^°),  north  and  south  latitude;  here  no  place  has  ver- 
tical sunshine  on  any  day,  and  no  day  passes  without  a 
sunrise  and  a  sunset. 

If  zones  are  limited  by  the  mean  annual  isotherms  of 
70°  and  30°,  their  borders  are  much  more  irregular  than 
when  limited  by  sunshine. 

34.  Observations  of  the  Sun.  —  Records  of  thermometer 
readings  during  the  school  year  should  be  used  to  show 
the  general  fall  of  temperature  to  midwinter,  and  the 
general  rise  from  midwinter  to  midsummer.  These 
changes  of  temperature  should  be  connected  with  the 
changes  in  the  apparent  movement  of  the  sun.  In  late 
December  the  sun  rises  south  of  east  and  sets  south  of 
west ;  at  midday  it  reaches  but  a  moderate  altitude  above 


THE  ATMOSPHERE  49 

the  southern  horizon ;  at  this  time  the  duration  of  daylight 
is  less  than  twelve  hours  and  the  strength  of  the  sunshine 
is  reduced.  In  late  June  these  conditions  are  all  reversed. 
The  low  temperature  of  winter  is  thus  seen  to  depend  on 
the  weak  sunshine  of  short  days,  and  the  high  temperature 
of  summer  on  the  strong  sunshine  of  long  days.  The  ris- 
ing temperature  through  spring  results  from  the  strength- 
ening of  sunshine  in  the  lengthening  days ;  the  falling 
temperature  of  autumn,  from  the  weakening  sunshine  in 
the  shortening  days.     (See  Supplement.) 

35.  Change  of  Temperature  with  the  Seasons.  —  An 
observer  at  any  one  place  notes  the  familiar  succession  of 
the  seasons  during  the  coui*se  of  the  year.  A  better 
understanding  of  the  meaning  of  the  seasons  may  be 
gained  if  the  earth  as  a  whole  is  considered,  as  on  the 
above  charts.  It  is  then  seen  that  for  a  time  the  heat 
equator  moves  a  moderate  distance  from  the  geographic 
equator  into  the  summer  hemisphere,  while  the  high  tem- 
peratures of  the  torrid  zone  advance  into  the  temperate 
zone,  and  the  rigor  of  polar  cold  is  somewhat  lessened ;  in 
the  other  hemisphere  the  polar  cold  is  extreme,  low  tem- 
peratures advance  over  the  temperate  zone,  and  the  heat 
on  the  border  of  the  torrid  zone  is  decreased. 

In  the  next  half  year  the  heat  equator  moves  slowly 
back  and  crosses  the  geographic  equator,  and  all  these  con- 
ditions are  reversed.  The  year,  or  period  in  which  the 
earth  revolves  around  the  sun  and  in  which  the  change  of 
seasons  therefore  take  place,  thus  comes  to  be  a  natural 
measure  of  time. 


50      ELEMENTARY  PHYSICAL  GEOGRAPHY 

36.  January  and  July  Isotherms.  —  The  general  distri- 
bution of  mean  temperatures  for  January  and  for  July  is 
shown  in  charts  of  monthly  isotherms,  Figures  18  and  19, 
on  which  the  following  exercise  may  be  based. 

Exercise.  In  which  summer  hemisphere  does  the  heat  equator 
stand  farther  from  the  geographic  equator  ?  Does  the  heat  equator 
stand  farther  from  the  geographic  equator  on  the  oceans  or  on  the 
lands?  Where  do  midsummer  temperatures  of  more  than  90° 
occur?  In  which  hemisphere  do  they  cover  the  largest  area?  What 
is  the  lowest  mean  temperature  in  January  ?     Where  does  it  occur  ? 

About  how  much  difference  is  there  between  January  and  July 
temperatures  in  latitude  40°  S.  ?  Where  in  latitude  40°  N.  is  there 
a  strong  difference  between  January  and  July  temperatures  ? 

37.  Mean  Annual  Range  of  Temperature.  —  The  average 
change  of  temperature  with  the  seasons  may  be  best 
studied  by  taking  the  difference  between  the  mean  temper- 
atures of  January  and  July.  This  difference  is  called  the 
mean  annual  range  of  temperature.  It  is  shown  for  the  dif- 
ferent parts  of  the  world  in  Figure  20.  The  range  is  gen- 
erally less  than  10°  over  the  torrid  oceans  and  less  than 
20°  over  most  of  the  temperate  oceans.  On  land  the  range 
increases.  Places  in  the  interior  of  continents  have  a  much 
stronger  range  than  those  on  continental  borders  or  islands. 

Central  Australia  and  the  interior  of  the  Sahara  have  a 
range  of  over  30°.  Over  most  of  the  United  States  the 
range  is  from  30°  to  60°.  Over  a  belt  of  land  from  Hudson 
bay  into  Alaska  the  range  is  more  than  80°.  Over  the 
greater  part  of  Europe-Asia  the  range  exceeds  40°. 

In  regions  of  the  greatest  range  the  winters  are  so  cold 
that  the  ground  is  frozen  to  a  depth  of  100  feet  or  more. 


Fig.  18.    Chart  of  Mean  Temperatures  for  January 


Fig.  19.    Chart  of  Mean  Temperatures  for  July 


THE  ATMOSPHERE 


51 


In  winter  ice  is  so  hard  that  the  runner  of  a  skate  does 
not  hold  upon  it;  wood  is  too  hard  to  be  chopped  with 
an  ax.  In  summer  thawing  reaches  only  a  few  feet 
below  the  surface.  Trees  gain  only  a  stunted  growth  or 
are  altogether  wanting. 

Compare  the  annual  range  on  the  western  and  eastern 
coasts  of  the  continents  in  temperate  latitudes.    On  which 


LIMES  or 
EQUAL  ATTKUAL  RANGB 
OF  TEMPERATCRK.     ' 

I \ L 


'  "-^  -  ••'m 


Fig.  20.    Chart  of  Annual  Range  of  Temperature 


coast  is  the  range  of  less  amount  ?  The  difference  of  range 
is  due  to  the  prevailing  westerly  winds,  which  carry  the 
nearly  uniform  conditions  of  the  ocean  on  to  the  western 
coasts,  and  the  changing  conditions  of  the  continental 
interior  out  to  the  eastern  coast. 

Exercise.  Where  is  the  greatest  annual  range?  What  is  its 
amount?  Compare  the  annual  range  of  Labrador  and  England,  of 
Virginia  and  Spain,  of  Japan  and  California. 


52      ELEMENTARY  PHYSICAL  GEOGRAPHY 

The  annual  changes  of  temperature  are  much  more  dis- 
tinct in  the  northern  hemisphere,  where  there  is  much 
land,  than  in  the  southern,  where  there  is  much  ocean. 
This  is  because  the  land  surface  changes  its  temperature 
more  easily  than  the  ocean  surface,  and  therefore  the  air 
over  the  land  becomes  hot  in  summer  and  cold  in  winter. 
The  change  of  seasons  in  the  north  temperate  zone, 
especially  on  the  lands,  is  much  stronger  than  in  the  south 
temperate  zone.  This  is  because  the  northern  continents 
are  broad  in  temperate  latitudes,  while  the  southern  are 
relatively  narrow. 

Exercise.  In  Figure  20  follow  the  latitude  circle  of  40°  or  50°  N. 
around  the  earth.  For  how  many  degrees  of  longitude  does  it  lie 
on  the  continents?  How  many  on  the  oceans?  Do  the  same  for 
latitudes  40°  or  50°  S.     Compare  the  results. 

Winter  and  summer  are  not  very  different  over  the  great 
oceans  of  the  south  temperate  zones,  where  the  weather 
is  rather  uniformly  chill  and  damp,  or  inclement,  all  the 
year  round.  This  is  because  water  is  slow  to  change  its 
temperature  ;  the  ocean  waters  and  the  air  over  them  suffer 
small  changes  of  temperature  during  the  year. 

In  the  temperate  zone  the  summer  half  year  is  the  time 
of  plant  growth,  and  is  therefore  the  season  of  greater 
activity  in  all  industries  immediately  connected  with  agri- 
culture. One  of  the  most  interesting  consequences  of  the 
advance  of  spring  and  summer  temperatures  into  higher 
latitudes  is  the  northward  passage  of  migratory  birds, 
familiar  to  every  lover  of  outdoor  nature.  The  approach 
of  winter  is  accompanied  by  the  return  of  the  birds  to 
warmer  latitudes. 


THE  ATMOSPHERE 


63 


38.  Terrestrial  Winds.  —  The  strength  of  the  planetary 
circulation  and  the  boundaries  of  its  wind  belts  vary  with 
the  seasons.  Thus  modified,  the  winds  may  be  called 
terrestrial,  as  belonging  to  the  earth  in  particular  with  its 
winters  and  summers,  instead  of  to  the  other  planets  which 
may  not  have  seasons  like  ours. 


Fig.  21.    Diagrams  of  Terrestrial  Winds  for  January  and  July 


Figure  21  gives  a  general  scheme  of  the  winds  for  January  and 
July,  without  considering  the  irregular  winds  produced  by  the 
continents  and  their  mountain  ranges.  The  heavier  lines  show 
the  stronger  winds!  In  which  month  are  the  winds  strongest  in 
the  northern  hemisphere?  In  what  season  is  this?  Answer  the 
same  questions  for  the  summer  hemisphere.  In  .what  season  are  the 
prevailing  westerlies  most  interrupted  by  spiraling  winds  (cyclones 
and  anticyclones)? 

Examine  the  isotherms  in  the  northern  hemisphere  for  January 
and  July,  Figures  18  and  19.  In  which  month  are  the  lines  closer 
together?  How  can  you  tell  from  this  in  which  month  there  is  the 
greatest  difference  of  temperature  between  the  torrid  zone  and  the 
Arctic  regions?     In  which  month  would  you  expect   the   general 


54 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


circulation  in  the  northern  hemisphere  to  be  the  stronger  ?  Why  ? 
Answer  the  same  questions  for  the  southern  hemisphere.  Compare 
the  results  for  the  two  hemispheres. 

It  is  thus  seen  that  in  winter  the  difference  of  tempera- 
ture between  the  equator  and  high  latitudes  is  strength- 
ened. As  the  general  circulation  of  the  atmosphere 
depends  on  this  difference,  the  winds  will  generally  be 


Fig.  22.    Winds  of  January 

stronger  in  winter  than  in  summer.  Tiiis  is  especially 
true  of  the  prevailing  westerlies  and  their  spiraling 
cyclonic  winds  in  the  northern  hemisphere ;  they  fre- 
quently become  stormy  in  winter,  while  they  are  rela- 
tively light  in  summer.  In  the  southern  hemisphere 
these  changes  ^re  less  marked.     Why  so  ? 

Examine  in  Figure  21  the  belts  of  light  breezes  and  occasional 
calms  between  the  trades  and  the  westerlies.  What  is  the  name  of 
these  belts?     Compare  their  positions  in  January  and  July.     What 


^ 


THE  ATMOSPHERE 


55 


is  the  name  of  the  belt  of  calms  and  light  breezes  between  the  trade 
winds  ?     How  does  its  position  change  with  the  seasons  ? 

The  horse  latitudes  and  equatorial  calms  are  much  less 
regular  in  reality  than  they  are  represented  in  Figure  21, 
on  account  of  the  irregular  outline  and  form  of  the  lands. 
A  better  illustration  of  the  prevailing  winds  for  January 
and  for  July  is  given  in  Figures  22  and  23. 


Fig.  23.    Winds  of  July 

The  light  and  irregular  winds  of  the  horse  latitudes 
migrate  toward  the  equator  in  the  winter  of  their  hemi- 
sphere, and  toward  the  pole  in  the  summer ;  these  belts  of 
migration  are  known  as  the  northern  and  southern  subtropi- 
cal belts  (*S^T,  Figure  21).  Any  country  over  which  a  sub- 
tropical belt  is  stretched  will  have  the  westerlies  and  their 
rainy  stoims  in  winter  and  the  drying  trades  in  summer. 
This  is  the  case  with  southern  California  and  the  Mediter- 
ranean countries  of  southern  Europe  and  northern  Africa,  as 


56  ELEMENTARY  PHYSICAL  GEOGRAPHY 

well  as  with  central  Chile,  southern  Africa,  and  south- 
ern Australia.  These  countries  are  said  to  have  a  sub- 
tropical climate.  In  what  months  will  they  have  their 
rainy  season? 

As  countries  in  the  subtropical  belts  are  dry  in  the 
growing  season,  agriculture  there  generally  requires  the 
aid  of  irrigation  (watering  the  fields  by  canals  led  from 
streams  or  reservoirs). 

Like  the  calms  of  the  horse  latitudes,  the  calms  and 
rains  of  the  doldrums  also  migrate  north  and  south  dur- 
ing the  year.  The  belt  of  winds  and  rainfall  thus  con- 
trolled forms  the  subequatorial  belt  (SQ,  Figure  21).  The 
migration  of  these  three  belts  follows  the  migration  of 
the  sun. 

The  plains  of  the  Orinoco  in  Venezuela,  north  of 
the  equator,  receive  -a  plentiful  rainfall  in  July  and 
August,  but  in  December  and  January  they  are  relatively 
dry.  In  the  wet  season  cattle  find  abundant  pasture 
on  the  plains,  but  in  the  dry  season  they  are  driven 
into  the  valleys.  On  the  plains  between  the  headwaters 
of  the  Amazon  and  the  Parana,  south  of  the  equator,  the 
months  of  wet  and  dry  seasons  are  reversed  from  those 
of  Venezu-ela. 

The  western  Sahara,  between  the  reach  of  the  subtropical 
(winter)  rains  on  the  north  and  the  subequatorial  (summer) 
rains  on  the  south,  gives  no  important  river  to  the  Atlantic 
along  a  thousand  miles  of  coast  line.  The  rise  of  the 
Nile  in  Egypt  from  June  to  September  results  from  the 
northward  advance  of  the  equatorial  rains  over  the  upper 
part  of  this  river  basin,  as  in  Figure  23. 


THE  ATMOSPHERE 


57 


39.  Monsoons.  —  In  the  belt  over  which  the  equatorial 
calms  move  north  and  south  during  the  year  the  trade 
winds  change  their  direction  in  the  warmer  and  cooler  half 
years.     Winds  of  this  kind  are  called  monsoons. 

How  do  the  winds  blow  in  the  northern  half  of  the  subequato- 
rial  belt  (6"^,  Figure  21) 
in   January?    in   July? 
how    in    the     southern 
half? 

What  parts  of  the 
equator  are  crossed  by 
the  extended  northeast 
trades  in  January,  Fig- 
ure 22?  by  the  ex- 
tended southeast  trades 
in  July,  Figure  23? 
Where  do  these  ex- 
tended winds  cover  the 
greatest  area? 

Note  in  Figure  24  the 
change  in  the  direction 
of  the  northeast  trades 
in  January  as  they  cross 
the  geographical  equa- 
tor and  enter  the  south- 
ern hemisphere  on  their 
way  to  the  calm  belt. 
What  is  the  direction 
of  the  wind  in  the  same 

part  of  the  southern  hemisphere  in  July?     Note  the  corresponding 
change  in  the  extended  southeast  trades  for  July  in  Figure  25. 

The  reason  for  this  change  of  direction  as  the  winds  cross 
the  equator  is  found  in  the  earth's  rotation,  on  account  of 


Fig.  24.    January  Monsoons  in  Indian  Ocean 


Fig.  25.    July  Monsoons  in  Indian  Ocean 


68     ELEMENTARY  PHYSICAL  GEOGRAPHY 

which  all  winds  in  the  northern  hemisphere  tend  to  turn  to 
the  right,  and  in  the  southern  hemisphere  to  the  left.  On 
account  of  the  irregular  distribution  of  land  and  water  mon- 
soons are  not  evenly  developed  all  around  the  equator. 

The  monsoons  of  the  Indian  ocean  are  the  most  remark- 
able of  the  world.  In  January  a  belt  of  northwest  mon- 
soon winds  is  developed  for  about  ten  degrees  south  of  the 
equator,  as  in  Figure  24.  In  July,  when  the  heat  equator 
has  shifted  far  northward  to  the  border  of  Asia,  a  broader 
belt  of  southwest  monsoon  winds  is  developed  north  of 
the  equator,  as  in  Figure  25. 

The  primitive  sailing  vessels  of  the  Indian  ocean  in 
earlier  centuries,  poorly  adapted  for  sailing  against  the 
wind,  made  voyages  only  as  the  monsoons  favored  their 
courses,  going  outward  from  India  to  Africa  in  one  half 
year  and  returning  in  the  next. 

The  east  coast  of  the  Malay  peninsula  is  beaten  by  heavy 
surf  under  the  northeast  monsoon,  and  then  the  native  fish- 
ermen stay  ashore.  But  under  the  southwest  monsoon, 
an  offshore  wind,  the  water  is  comparatively  smooth,  and 
large  fleets  of  fishing  boats  put  out  to  sea  with  their 
palm-leaf  sails. 

In  what  months  would  the  events  described  in  the  two  preceding 
paragraphs  be  expected  ? 

40.  Winds  of  the  Continents.  —  As  the  air  over  the  con- 
tinents is  warmer  than  that  over  the  neighboring  oceans 
in  summer  and  colder  in  winter,  the  winds  tend  to  blow 
inward  toward  continental  centers  in  summer  and  outward 
from  them  in  winter. 


THE  ATMOSPHERE  69 

In  the  north  temperate  zone  the  cold  land  winds  of 
winter  tend  outward  toward  the  sea,  and  the  far  inland 
regions  have  much  clear  and  dry  weather.  In  summer 
the  warm  and  moist  sea  winds  tend  inward  toward  the 
still  warmer  lands,  and  the  interior  parts  of  the  large  con- 
tinents then  have  a  greater  abundance  of  clouds  and  rain. 

The  general  circulation  of  the  atmosphere  is  much  com- 
plicated by  this  outward  and  inward  tendency  of  the  winds 
over  the  continents,  as  may  be  seen  by  comparing  the 
winds  of  January  and  July  over  Asia,  Figures  22  and  23, 
with  the  winds  of  corresponding  latitudes  in  Figure  21. 
The  regular  belts  of  winds  in  the  latter  figure  are  much 
broken  up,  especially  in  the  northern  hemisphere. 

41.  Winds  on  Land.  —  The  lower  winds  are  generally 
not  so  strong  or  so  regular  on  the  uneven  lands  as  on  the 
level  seas,  although  the  upper  currents  over  the  lands  still 
flow  rapidly.  In  valleys  the  winds  are  much  influenced 
by  the  direction  of  the  inclosing  slopes.  Hence  observers 
living  in  deep  valleys  may  often  determine  the  general 
direction  of  the  winds  better  by  watching  the  drift  of  the 
clouds  than  by  noting  the  position  of  their  wind  vanes. 

The  air  over  the  lands  is  cooler  and  therefore  heavier 
than  that  over  the  sea  at  night,  but  warmer  and  lighter  by 
day.  Hence  around  the  border  of  the  lands  the  wind 
tends  to  blow  alternately  offshore  at  night  and  onshore  by 
day  for  a  short  distance  from  the  coast,  such  winds  being 
known  as  land  and  sea  breezes. 

On  the  coasts  in  the  torrid  zone  the  sea  breeze  is  wel- 
come, as  it  tempers  the  excessive  heat  of  the  day  on  land. 


60  ELEMENTARY  PHYSICAL  GEOGRAPHY 

The  same  is  true  of  summer  weather  in  the  temperate 
zone.  On  the  coast  of  Peru  the  fishermen  sail  offshore  in 
the  early  morning  with  the  land  breeze,  and  return  in  the 
afternoon  with  the  sea  breeze. 

42.  Daytime  Winds In  fair,  warm  weather  the  lower 

air  lying  on  the  land  becomes  unduly  heated  by  day,  as 
compared  with  the  overlying  air.  The  warmer  lower  air 
then  rises  and  the  cooler  upper  air  descends,  this  being  a 
small  example  of  convectional  circulation.  It  is  like  the 
movement  of  water  in  a  kettle  that  is  heated  at  the 
bottom. 

The  faster-moving  currents  from  aloft  are  thus  brought 
down  to  the  surface.  Hence  on  lands  the  winds  of  fair 
weather  in  the  daytime  are  commonly  stronger  than  those 
of  the  night.  This  is  prevailingly  the  case  through  the 
year  on  torrid  lands ;  on  the  temperate  lands  it  is  common 
during  summer  weather,  but  is  less  noticed  in  winter. 
Why  does  no  such  daily  change  in  the  strength  of  the 
wind  occur  at  sea? 

43.  Humidity.  —  The  condition  of  the  atmosphere  as  to 
the  water  vapor  that  it  contains  is  expressed  by  the  term 
humidity.  When  the  air  contains  much  vapor  and  feels 
damp  the  humidity  is  said  to  be  high.  When  it  con- 
tains little  vapor  and  feels  dry  the  humidity  is  low.  The 
higher  the  temperature  of  the  air,  the  greater  the  amount 
of  vapor  it  may  contain.  When  as  much  vapor  is  present 
as  is  possible  at  a  given  temperature  the  air  is  said  to  be 
in  the  state  of  saturation.  The  lower  air  over  the  ocean 
is  usually  almost  saturated ;  in  the  doldrums  the  humidity 


THE  ATiMOSPIIERE  61 

is  always  high.  Far  inland,  in  the  desert  regions  of  con- 
tinents, the  air  may  contain  very  little  vapor;  here  the 
humidity  is  low.  Dry  air  is  more  agreeable  than  damp, 
because  it  allows  active  evaporation  from  the  skin.  Cold 
damp  air  is  chilly  and  "  penetrating."  Warm  damp  air  is 
sultry  and  "  close." 

44.  Dew  and  Frost.  —  Dew  is  a  deposit  of  moisture  on 
the  ground,  or  on  loose  objects  like  leaves  and  sticks  lying 
on  the  ground.  It  is  formed  when  the  ground  is  cooled 
at  night  by  radiation ;  then  the  air  near  it  is  chilled  by 
conduction,  and  some  of  the  water  vapor  in  the  air  is 
changed  to  the  liquid  form.  The  temperature  at  which 
dew  begins  to  be  foi-med  in  cooling  air  is  called  the  dew- 
point. 

Exercise.  The  dew-point  may  be  determined  by  experiment  as 
follows :  Half  fill  a  tin  cup  with  water  whose  temperature  is  about 
like  that  of  the  air.  Then  slowly  pour  in  ice  water,  stirring  it  with 
a  thermometer.  As  the  cup  is  cooled  the  air  next  to  it  is  cooled 
also.  As  the  air  is  cooled  the  vapor  that  it  contains  will  more  and 
more  nearly  saturate  it.  When  the  outer  surface  of  the  cup  is  first 
clouded  by  a  deposit  of  moisture  the  air  next  to  it  has  just  passed 
the  condition  of  saturation,  and  the  temperature  of  the  water  gives  a 
close  indication  of  the  dew-point.  If  ice  is  added  so  as  to  make  the 
water  still  colder,  more  and  more  vapor  will  be  condensed  on  the 
cup,  the  air  constantly  being  saturated  with  the  vapor  that  remains 
in  it  as  its  temperature  falls. 

When  moisture  is  condensed  upon  the  ground  at  tem- 
peratures below  the  freezing  point  it  forms  frost.  Thus 
frost  on  the  ground  corresponds  to  snow  in  the  air,  and 
dew  corresponds  to  rain. 


62      ELEMENTARY  PHYSICAL  GEOGRAPHY 

Dew  and  frost  are  in  part  supplied  from  water  vapor  in 
the  air  that  lies  near  the  ground,  in  part  by  vapor  that  rises 
through  the  soil  from  its  deeper  and  moister  parts.  In  the 
daytime  the  vapor  from  the  soil  escapes  into  the  warm  air ; 
but  at  night,  when  the  ground  is  colder  at  the  surface  than 
beneath,  the  rising  vapor  is  condensed.^  Dewdrops  found 
on  the  blades  of  grass  and  on  the  living  leaves  of  plants 
close  to  the  ground  are  in  large  part  supplied  by  the  water 
that  the  plants  bring  up  from  the  ground  through  the 
roots.  In  the  daytime  the  moisture  evaporates  from  the 
leaves,  but  at  night  it  may  collect  upon  them  in  drops. 

At  night,  when  the  air  is  calm  and  clear,  the  ground  is 
cooled  by  losing  its  heat  to  cold  outer  space;  the  quiet 
lower  air  is  then  chilled,  because  it  lies  on  the  cooled 
ground,  and  dew  (or  frost)  is  formed.  When  the  wind  is 
blowing  the  lower  air  is  constantly  changed  and  none  of 
it  is  much  chilled;  when  the  sky  is  cloudy  at  night  the 
ground  cools  but  little ;  hence  on  windy  or  cloudy  nights 
little  or  no  dew  (or  frost)  is  formed. 

45.  Clouds,  Fog,  and  Mist.  —  The  different  processes  by 
which  water  vapor  is  condensed  ^  in  the  atmosphere  pro- 
duce clouds  of  many  different  forms.  It  has  been  explained 
that  in  daytime  of  fair  summer  weather  the  lower  air  tends 
to  rise  in  convectional  currents.    The  ascending  air  currents 

1  It  should  be  noticed  that  the  term  condensation,  when  applied  to  vapor, 
refers  to  its  change  from  the  gaseous  to  the  liquid  (or  solid)  state,  and  not 
to  its  compression,  as  vapor,  into  a  smaller  volume.  Hence  condensation 
of  vapor  may  take  place  while  the  air  with  which  it  is  mixed  is  expanding, 
provided  that  the  expansion  produces  sufficient  cooling  to  lower  the  tem- 
perature below  the  dew-point. 


Pr.ATi:  in.      1>.    CiiTUs  C'l()ii(l> 


Plate  III.     A.  Cumulus  Clouds 


THE  ATMOSPHERE  68 

expand  and  cool  as  they  rise,  and,  if  their  ascent  is  great 
enough,  some  of  their  vapor  is  condensed,  fonning  round- 
topped  clouds,  brilliant  white  in  strong  sunshine,  as  in 
Plate  III,  A;  the  air  within  the  clouds  is  all  saturated 
by  the  vapor  it  still  contains.  The  clouds  are  of  unequal 
size,  but  have  their  bases  at  about  the  same  height  (com- 
monly one  fourth  to  one  half  of  a  mile),  and  all  drift 
along  with  the  speed  of  the  currents  in  which  they  are 
formed.  Their  rapid  motion  can  be  recognized  by  watch- 
ing their  shadows  pass  across  a  field ;  they  nearly  always 
drift  eastward  in  the  United  States,  being  borne  in  the 
prevailing  westerly  winds  of  middle  latitudes. 

Clouds  of  this  kind  are  called  cumulus  (heap)  clouds. 
They  usually  begin  to  form  in  the  warming  morning  hours 
of  fair  weather,  but  dissolve  and  disappear  in  the  late 
afternoon,  when  sunshine  weakens,  the  ground  cools,  and 
convection  ceases. 

It  is  usually  the  case  that  the  great  cyclonic  storms  of 
the  westerly  winds  are  preceded  by  long  filmy  or  feathery 
strips  of  pale  whitish  cloud,  as  in  Plate  III,  B.  Clouds  of 
this  kind  are  formed  at  a  height  of  several  miles,  in  the  air 
currents  that  flow  out  and  forward  from  the  upper  part  of 
the  storm.  They  are  called  cirrus  (curl)  clouds.  They  con- 
sist of  minute  ice  crystals,  because  the  moisture  forming 
them  has  been  condensed  in  the  cold  upper  air  at  tempera- 
tures below  the  freezing  point.  Sometimes  the  cirrus  is 
spread  out  in  a  thin  sheet  called  cirro-stratus.  When  the 
sun  or  moon  is  seen  through  a  cirro-stratus  a  large  ring 
faintly  colored  with  red  on  the  inside  is  seen  around  the 
luminary.     Such  a  ring  is  called  a  halo ;  it  is  formed  by 


64  ELEMENTARY  PHYSICAL  GEOGRAPHY 

the  bending  (refraction)  of  the  light  in  passing  through  the 
ice  crystals.  Halos  are  common  and  brilliant  in  the  polar 
regions. 

In  the  central  parts  of  the  great  whirling  cyclonic  storms 
heavy  dull-gray  cloud  sheets  of  great  size  are  formed 
at  a  moderate  height  above  the  earth's  surface  by  the 
gradual  cooling  of  the  inflowing  winds.  Clouds  of  this 
kind,  from  which  rain  or  snow  falls,  are  called  alto-nimhus 
and  nimbus,  A  nimbus  cloud  is  shown  on  the  right  side 
of  Plate  IV.  As  with  other  clouds,  the  air  within  the 
nimbus  is  constantly  saturated.  These  clouds  often  cover 
the  area  of  several  states  at  once,  and  they  may  hide 
the  sun  and  stars  for  several  days  at  a  time,  yielding 
plentiful  rain  or  snow  before  they  drift  away  eastward 
and  reveal  the  clear  sky  again  in  fair  weather.  They  are 
especially  large  and  heavy  in  winter,  when  the  westerly 
winds  and  their  storms  are  stron-gest.  When  the  sun  or 
moon  is  seen  through  the  fragments  of  nimbus  clouds  it  is 
often  closely  surrounded  by  a  brilliant  glow,  called  a  corona. 

When  a  cloud  is  formed  at  so  low  a  level  that  it  rests 
on  the  ground  or  on  the  sea  surface  it  is  called  fog.  This 
is  often  the  case  when  moist  sea  winds  of  mild  temperature 
blow  across  a  colder  part  of  the  sea  or  blow  inland  over 
snow-covered  hills.  Fog  is  often  formed  in  valleys  among 
mountains  by  the  cooling  of  the  lower  air  at  night.  Fog 
of  this  kind  usually  disappears  in  the  morning  sunshine, 
but  if  very  heavy  it  may  not  be  dissolved  by  the  short  and 
weak  sunshine  of  a  winter  day. 

A  slight  cooling  of  damp  air  may  produce  a  faint  cloudi- 
ness, known  as  mist,  much  less  dense  than  fog. 


THE  ATMOSPHERE  66 

46.  Thunderstorms.  —  When  the  lower  air  is  warm  and 
moist  it  is  apt  to  rise  and  form  great  cumulus  clouds  from 
ten  to  fifty  miles  in  length,  whose  tops  may  reach  heights 
of  more  than  a  mile.  When  the  rising  movement  is  active 
and  the  cloud  grows  to  great  size  it  may  often  be  seen  to 
spread  out  at  the  top  in  a  cirro-stratus  film,  and  about  the 
same  time  rain  falls  from  its  base.  If  the  rain  becomes 
heavy,  lightning  flashes  occur,  causing  peals  of  thunder; 
hence  such  storms  are  called  thunderstorms. 

Storms  of  this  kind  are  common  in  the  cloudy  belt  of 
the  doldrums,  where  they  usually  occur  in  the  afternoon 


Fig.  26.    A  Distant  Thunderstorm 

and  evening.  They  are  also  common  on  the  lands  in 
periods  of  hot  summer  weather.  Much  of  the  summer 
rain  in  the  Mississippi  valley  falls  from  thunderstorms 
which  drift  eastward  in  the  afternoon  and  night  at  a  rate 
of  twenty  or  thirty  miles  an  hour,  giving  heavy  rainfall  for 
an  hour  or  two  as  they  pass  by.  A  violent  blast  of  wind, 
or  thunder  squall,  often  rushes  forward  from  beneath  the 
front  of  the  cloud  mass,  raising  a  cloud  of  dust  before  the 
rain  arrives. 

During  the  growth  of  a  thunderstorm  cloud  the  water 
particles  in  it  become  charged  with  electricity.  When  the 
drops  become  large  enough  to  fall  as  rain  the  electricity 
is  discharged  from  one  part  of  the  cloud  to  another,  or  from 


66  ELEMENTARY  PHYSICAL  GEOGRAPHY 

the  cloud  to  the  ground,  in  a  great  electric  spark,  or  light- 
ning flash.  Thunder  is  the  sound  caused  by  the  violent 
agitation  of  the  air  along  the  flash.  It  may  be  compared 
to  the  sound  caused  by  snapping  a  whip.  As  sound  travels 
through  the  air  at  the  rate  of  a  mile  in  five  seconds,  the 
distance  of  a  flash  can  be  determined  in  miles  by  counting 
the  number  of  seconds  between  the  lightning  and  its 
thunder  clap  and  dividing  the  number  by  five.  The 
"rolling"  of  thunder  is  caused  partly  by  the  continuous 
arrival  of  the  sound  from  different  parts  of  a  long  flash, 
partly  by  the  echoing  from  clouds  or  from  hills  and  moun- 
tains. At  night  the  upper  clouds  of  distant  thunderstorms 
are  illuminated  by  flashes,  commonly  called  heat  lightning, 
too  far  away  for  the  thunder  to  be  heard. 

An  unusually  heavy  and  violent  rain,  popularly  known 
as  a  cloud-burst,  sometimes  falls  during  a  thunderstorm 
upon  a  small  district.  If  on  a  hillside  it  may  wash  away 
the  soil,  baring  the  rock  beneath. 

47.  The  Rainbow.  —  When  a  thunderstorm  passes  east- 
ward in  the  late  afternoon  a  rainbow  is  usually  seen  by 
observers  on  the  west  of  it.  The  bow  is  formed  by  the  sun- 
light that  is  turned  back  and  bent  (refracted)  by  the  drops 
that  are  falling  from  the  rear  of  the  cloud.  The  center  of 
the  bow  will  be  directly  opposite  the  sun.  Why  will  a 
rainbow  form  a  half  circle  at  sunset?  Why  does  a  rain- 
bow usually  show  less  than  a  half  circle  ?  A  bow  forming 
a  complete  circle  might  be  seen  from  a  balloon. 

48.  Tornadoes  and  Waterspouts.  —  Violent  whirlwinds 
are  occasionally  formed  in  thunderstorms.    They  are  seldom 


pi 
O 


o 


THE  ATMOSPHERE  67 

more  than  a  quarter  of  a  mile  in  diameter ;  they  drift  along 
with  the  thunderstorm  in  which  they  are  formed,  usually 
in  an  easterly  direction,  passing  by  in  a  minute  or  two. 
Their  whirling  winds  are  strong  enough  to  blow  down 
trees  and  overturn  building^.  Violent  local  storms  of  this 
kind  are  often  called  cyclones,  or  prairie  twisters,  in  the 
Mississippi  valley,  but  the  name  tornado  is  to  be  preferred 
in  order  to  distinguish  them  from  the  much  larger  and  less 
violent  cyclonic  storms. 

When  violent  whirlwinds  of  this  kind  occur  over  a 
water  surface  a  watery  column  is  formed  in  their  vortex ; 
they  are  then  called  waterspouts.  Plate  IV  shows  a  water- 
spout over  Vineyard  sound,  southeastern  Massachusetts, 
as  photographed  on  Aug.  19,  1896.  A  vessel  overtaken 
by  such  a  whirlwind  may  be  suddenly  dismasted. 

49.  .Tropical  Cyclones  (Hurricanes  and  Typhoons). — 
Violent  storms  known  as  tropical  cyclones  are  occasionally 
developed  in  the  doldrums  when  the  heat  equator  stands 
farthest  from  the  geographical  equator.  They  appear  to 
be,  like  thunderstorms,  due  to  the  inflow,  ascent,  and  out- 
flow of  very  warm  moist  air.  They  grow  to  be  several 
hundred  miles  in  diameter,  with  violent  winds,  whirling  in 
great  spirals  around  a  center  of  low  barometric  pressure, 
great  cloud  sheets,  and  heavy  rains. 

As  in  the  cyclonic  storms  of  temperate  latitudes,  the 
winds  of  tropical  cyclones  turn  counter-clockwise  in  the 
northern  and  clockwise  in  the  southern  hemisphere.  As 
tropical  cyclones  increase  in  size,  they  travel  slowly  (one 
or  two  hundred  miles  a  day)  westward  and  toward  the 


68 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


temperate  zone  near  the  western  border  of  their  ocean.  In 
a  week  or  ten  days  they  pass  from  the  trade-wind  belt  into 
the  prevailing  westerlies.  As  they  enter  the  temperate 
zone,  still  increasing  in  size  but  usually  decreasing  in 
violence,  their  path  curves  eastward,  and  they  join  the 
great  procession  of  cyclonic  storms  of  middle  and  higher 


Fig.  27.    Regions  of  Tropical  Cyclones 

latitudes.     The  chief  regions  of  these  storms  are  shown 
by  dotted  areas  in  Figure  27. 

In  the  southern  hemisphere  the  doldrums  of  the  Atlantic 
hardly  pass  south  of  the  equator,  on  account  of  the  large 
supply  of  cooled  water  that  comes  northward  west  of 
Africa ;  hence  no  tropical  cyclones  occur  on  the  Brazilian 
coast.  In  the  western  Pacific  ocean  the  doldrums  are 
farthest  south  in  February  and  March,  and  at  that  time 
cyclones  occur  in  the  region  of  the  Fiji  islands.  In  the 
southern  Indian  ocean  cyclones  occur  in  the  same  months 
east  of  Madagascar. 


THE  ATMOSPHERE  69 

In  the  northern  hemisphere  the  doldrums  are  farthest 
north  in  the  western  Atlantic  and  Pacific  in  August  and  Sep- 
tember ;  cyclones  occur  in  these  months  in  the  West  Indies, 
where  they  are  commonly  called  hurricanes,  and  in  the  region 
of  the  Philippines,  where  they  are  known  as  typhoons.  In 
the  Indian  ocean  there  are  two  seasons  when  the  doldrums 
stand  over  the  warm  seas  between  the  equator  and  Asia : 
one  in  May,  as  the  doldrums  are  moving  north;  one  in 
October,  when  they  are  moving  south ;  hence  in  this  ocean 
alone  there  are  two  seasons  when  tropical  cyclones  occur. 

Formerly  much  destruction  was  wrought  on  vessels  at 
sea  by  the  furious  winds  of  tropical  cyclones ;  but  now 
that  the  season  of  occurrence,  the  usual  path,  and  the 
behavior  of  the  winds  of  hurricanes  have  been  learned,  and 
now  that  vessels  are  built  larger  and  stronger,  losses  at  sea 
are  much  less  serious  than  they  were  a  century  ago. 

When  hurricane  winds  blow  over  islands  in  the  torrid 
oceans  they  may  cause  much  damage  to  vessels  in  the 
harbors  by  driving  them  ashore,  and  to  settlements  by 
destroying  the  houses  and  plantations.  Cocoanut  palms 
may  thus  be  stripped  of  their  leaves,  after  which  the  trees 
require  a  number  of  years  of  growth  before  again  bearing 
the  fruit  of  which  so  many  uses  are  made. 

The  great  sea  floods  by  which  Galveston,  Texas,  was 
devastated  in  September,  1900,  were  caused  by  the  winds 
of  a  tropical  cyclone  which  brushed  the  surface  waters 
from  the  Gulf  of  Mexico  into  the  streets  of  the  city. 
Similar  sea  floods  have  repeatedly  occurred  on  the  low- 
lands at  the  head  of  the  Bay  of  Bengal,  drowning  many 
thousands  of  the  people. 


70     ELEMENTARY  PHYSICAL  GEOGRAPHY 

50.  Rainfall. — Rain,  snow,  hail,  and  sleet  are  all  included 
under  the  general  term  rainfall.  The  explanation  already 
given  in  Section  30  has  shown  how  closely  the  amount  and 
season  of  rainfall  are  connected  with  the  circulation  of  the 
atmosphere. 

Snow  occurs  when  the  moisture  of  the  air  is  condensed 
at  temperatures  below  the  freezing  point  (32°).  Snow 
flakes  are  six-rayed  ice  crystals  of  various  patterns.  Rain 
occurs  when  the  moisture  of  the  atmosphere  is  condensed 
into  drops  at  temperatures  above  the  freezing  point,  or 
when  the  snow  flakes  of  lofty  clouds  descend  into  the 
warmer  lower  atmosphere  and  melt  before  reaching  the 
groimd.     Sleet  is  half-melted  snow. 

•  Hail  is  a  mixture  of  ice  and  snow,  usually  in  rounded 
pellets,  sometimes  half  an  inch,  rarely  an  inch,  in  diameter. 
It  occurs  chiefly  in  summer,  when  the  ascending  currents 
of  lofty  thunderstorms  carry  raindrops  so  far  upward  that 
they  are  frozen  and  coated  with  snow  before  they  fall. 
Hailstorms  occasionally  do  much  damage  to  crops  and 
buildings. 

Hail  should  not  be  confounded  with  the  little  pellets  of 
nearly  transparent  ice,  properly  called  frozen  rain,  caused 
by  the  fall  of  raindrops  from  a  cloud  whose  temperature 
is  above  32°  through  a  lower  stratum  of  freezing  air. 
Hail  occurs  chiefly  in  hot  summer  weather;  frozen  rain 
in  winter. 

The  amount  of  rain  is  determined  by  measuring  the 
depth  of  water  that  is  collected  in  a  cylindrical  vessel 
having  vertical  sides,  called  a  rain  gauge.  The  gauge 
should  be  set  in  an   open   space,   away  from  trees   and 


THE  ATMOSPHERE  71 

buildings.  Snow  should  be  melted  before  it  is  measured. 
Eight  or  ten  inches  of  snow  correspond  to  about  an  inch 
of  rainfall.  An  annual  total  of  eighteen,  twenty,  or  more 
inches  is  necessary  for  agriculture,  as  over  the  great  prairie 
region  of  the  Mississippi  and  Ohio  valleys  from  the  95th 
meridian  eastward.  If  the  annual  amount  is  between 
eighteen  and  ten  inches,  agriculture  requires  irrigation,  as 
on  a  large  part  of  the  Great  plains  east  of  the  Rocky  moun- 
tains, and  over  large  areas  in  the  basins  of  Utah  and  Nevada ; 
but  scattered  grass  sufficient  for  cattle  ranges  may  grow  in 
such  regions.  If  the  annual  total  is  under  twelve  or  ten 
inches,  there  will  not  be  water  enough  for  irrigation,  unless 
it  is  supplied  by  rivers  that  rise  in  a  moister  climate,  as  in 
parts  of  Arizona  and  southeastern  California. 

The  distribution  of  the  annual  rainfall  over  the  world, 
represented  in  Figure  28,  shows  that  the  greater  amounts 
(eighty  inches  or  more)  occur  in  the  subequatorial  belt  and 
on  mountain  slopes  ascended  by  the  trade  winds  or  the  pre- 
vailing westerlies.  Most  of  the  dry  and  desert  regions  of 
the  world  (twenty  inches  of  rain  or  less)  are  either  low- 
lands of  the  trade-wind  belt,  like  the  Sahara  and  central 
Australia,  or  the  slopes  and  lowlands  to  the  leeward  of 
lofty  mountains,  as  in  Peru,  or  continental  interiors  crossed 
by  the  westerly  winds,  as  in  central  Asia. 

Exercise.  Where  are  the  regions  of  heaviest  rainfall  ?  How  are 
these  regions  related  to  the  belts  of  the  terrestrial  winds  ?  to  coast 
lines?  to  mountain  ranges?  Where  are  the  regions  of  light  rain- 
fall?    How  are  these  regions  related  to  the  terrestrial  winds? 

The  heaviest  rainfall  in  the  world  occurs  on  the 
southern  slopes  of  the  Himalayas,  north  of  the  Bay  of 


72     ELEMENTARY  PHYSICAL  GEOGRAPHY 

Bengal.  Here  the  rainfall  of  a  single  year  would  meas- 
ure thirty-five  or  forty  feet  in  depth,  and  much  more 
than  half  of  this  amount  falls  during  the  summer  half 
year  when  the  southerly  monsoon  is  blowing.  On  the 
bold  southwest  coast  of  India  an  annual  fall  of  over 
thirty  feet  occurs. 

The  greater  parts  of  western  Europe  and  of  eastern 
North  America  are  fortunate  in  receiving  a  plentiful  but 
not  excessive  rainfall. 

In  the  polar  regions  the  annual  snowfall,  melted,  would 
seldom  exceed  fifteen  inches  of  water,  and  would  fre- 
quently be  less  than  ten.  This  is  because  cold  air  can- 
not contain  much  vapor,  and  because  when  cold  air  is 
cooled  there  is  but  little  vapor  condensed  from  it.  In 
the  torrid  zone  the  equatorial  rains  are  heavier  because 
warm  air  can  contain  a  large  quantity  of  vapor,  and  when 
warm  air  is  cooled  it  yields  an  abundant  condensation 
of  moisture. 

51.  Rainfall  of  the  United  States.  —  The  rainfall  of  the 
United  States  may  be  considered  under  three  headings : 
the  Pacific  slope,  the  western  interior  region,  the  eastern 
region.  The  Pacific  slope  has  plentiful  rainfall  in  the 
north  (over  sixty  inches),  where  the  storms  of  the  west- 
erlies are  common ;  but  it  has  light  rainfall  in  the  south 
(under  thirty  inches),  because  here  the  westerlies  turn 
southward  to  join  the  trades,  and  storms  are  infrequent. 
The  westerly  winds  are  stronger  and  stormier  in  winter 
than  in  summer;  hence  the  rainfall  of  Washington  and 
Oregon  is  heavier  in   the   winter   than   in   the    summer 


THE  ATMOSPHERE  73 

months.  The  belt  of  westerly  winds  reaches  farther 
south  in  winter  than  in  summer;  hence  the  rainfall  of 
southern  California  is  almost  entirely  confined  to  the 
winter  months,  while  the  summers  are  very  dry,  thus 
illustrating  the  features  of  the  subtropical  belt. 


Fig.  29.    Annual  Rainfall  of  the  United  States 

Darkest  shade,  over  80  inches.  Lighter  vertical  lines,  from  40  inches  to  80  inches. 
Horizontal  lines,  from  20  inches  to  40  inches.  Blanlc,  from  10  inches  to  20 
inches.    Dotted,  less  than  10  inches. 


The  western  interior  region,  from  the  Cascade  and  Sierra 
Nevada  mountains  to  the  100th  meridian,  has  moderate  or 
plentiful  rainfall  on  the  mountains  and  high  plateaus,  be- 
cause the  air  is  cooled  and  some  of  its  moisture  is  con- 
densed as  the  westerly  winds  rise  over  these  elevations. 
The  lower  lands,  as  in  the  basins  of  Utah  and  Nevada 
and  over  the  Great  plains  that  slope  eastward  from  the 


74  ELEMENTARY  PHYSICAL  GEOGRAPHY 

Rocky  mountains,  have  light  rainfall.  The  winds  here, 
already  dried  by  losing  much  of  their  moisture  in  cross- 
ing the  ranges  farther  west,  are  seldom  cooled  enough  to 
form  clouds  and  to  yield  rain.  Hence  much  of  this  region 
is  arid.  A  large  part  of  Nevada,  Utah,  and  Arizona  is  too 
dry  to  yield  pasturage ;  elsewhere  a  thin  growth  of  grass 
suffices  to  support  cattle  if  they  have  a  large  area  over 
which  to  range.  Agriculture  is  seldom  successful  in 
this  region  without  the  aid  of  irrigation. 

The  eastern  region  is  not  distinctly  separated  from 
the  western;  the  rainfall  gradually  increases  eastward, 
as  moisture  is  supplied  in  greater  quantities  by  south- 
erly winds  from  the  Gulf  of  Mexico  and  from  the 
Atlantic.  Over  most  of  this  great  region  rainfall  is 
well  distributed  through  the  year  (over  forty  or  fifty 
inches) ;  somewhat  more  falls  in  summer  than  in  winter 
over  the  mid-Mississippi  basin.  The  heaviest  fall  (over 
sixty  or  eighty  inches)  is  on  the  states  bordering  the  Gulf 
of  Mexico  (not  including  Texas),  and  on  the  mountains 
of  North  Carolina. 

52.  Weather  Changes.  —  The  term  weather  includes  all 
the  atmospheric  conditions  that  an  observer  may  feel  or 
see,  —  hot  or  cold,  clear  or  cloudy,  dry  or  wet,  windy  or 
calm. 

In  the  torrid  zone  the  weather  is  marked  by  regular 
changes  from  day  to  night ;  the  changes  are  small  at  sea 
and  greater  on  land,  and  they  are  seldom  interrupted  by 
storms,  except  that  afternoon  thunderstorms  are  common 
in  the  belt  of  equatorial  rains.     In  the  summer  season  of 


THE  ATMOSPHERE  75 

temperate  latitudes  weather  changes  are  usually  of  mod- 
erate amount.  In  winter  the  weather  of  temperate  lati- 
tudes is  largely  controlled  by  the  passage  of  cyclonic  and 
anticyclonic  areas,  which  are  then  numerous  and  large, 
while  the  control  by  the  change  from  day  to  night  is  rela- 
tively weak. 

In  frigid  latitudes  the  change  of  weather  from  day  to 
night  is  always  weak  compared  with  the  changes  caused 
by  the  passage  of  the  great  atmospheric  whirls. 

The  relation  of  weather  changes  to  the  spiraling  winds 
of  the  prevailing  westerlies  may  be  simply  illustrated  by 
drawing  (on  an  appropriate  scale)  the  winds  and  clouds 
of  a  cyclonic  and  an  anticyclonic  area,  as  in  Figure  16,  on 
tracing  paper  and  moving  the  paper  slowly  to  the  right, 
across  a  map  of  the  United  States.  Let  the  center  of  the 
cyclonic  area  be  supposed  to  move,  for  example,  in  four 
days  from  Colorado  past  Lake  Michigan  and  down  the 
St.  Lawrence  river.  Note  the  changes  of  wuid  and 
weather  at  Indianapolis,  or  some  other  place,  as  the  spi- 
raling wind  areas  advance  eastward.  Consider  the  tem- 
perature of  the  regions  whence  the  winds  come  in  winter 
and  summer,  Figures  18  and  19,  and  infer  the  changes  of 
weather  that  they  will  bring.  In  the  diagram  for  winter 
weather  the  area  of  the  spiraling  winds  should  be  larger 
than  in  summer ;  the  cloud  sheet  about  the  cyclonic  center 
should  be  larger  and  the  winds  stronger. 

A  series  of  cyclonic  areas  sometimes  pass  by  at  the  rate 
of  two  in  seven  days,  thus  causing  a  repetition  of  a  certain 
kind  of  weather  on  the  same  day  of  the  week  for  several 
weeks  together. 


76  ELEMENTARY  PHYSICAL  GEOGRAPHY 

53.  Summer  Weather  in  the  United  States.  —  A  well- 
marked  series  of  weather  changes  over  the  central  and 
eastern  United  States  in  summer  may  open  with  fair 
weather  and  bright  blue  sky ;  the  days  are  warm  but  not 
oppressive;  the  nights  are  cool  and  refreshing.  Then,  if 
a  cyclonic  center  appears  a  thousand  miles  or  so  to  the 
west,  the  wind  changes  to  a  southerly  source,  so  that  it 
comes  from  the  warm  waters  of  the  Gulf  of  Mexico  and 
the  warmer  land  of  the  Southern  States.  The  air  becomes 
hazy  and  the  sky  pale  blue;  the  days  are  sultry  and 
oppressive,  and  the  nights  lose  their  refreshing  coolness; 
the  ground  is  dried  and  parched,  and  vegetation  suffers. 
The  great  corn  crop  of  the  Mississippi  valley  may  profit 
by  these  high  temperatures  if  they  do  not  last  too  long, 
but  manual  labor  is  exhausting  under  the  blazing  sun,  and 
sunstrokes  occur  in  increasing  numbers. 

Scattered  thunderstorms  are  then  reported  for  a  day  or 
two  in  the  afternoon  and  evening.  These  are  followed  by  a 
more  extended  cloudiness  as  the  cyclonic  center  approaches, 
and  general  rains  may  fall  over  several  states  near  the  low- 
pressure  center.  Thunderstorms  of  great  size  are  some- 
times formed  in  the  moist  southerly  winds,  occasionally 
giving  rise  to  destructive  tornadoes.  As  these  local  storms 
pass  by,  the  cooler  northwesterly  winds  in  the  rear  of  the 
low-pressure  center  come  from  the  far  northern  plains. 
The  clouds  drift  away  eastward,  the  pressure  slowly  rises, 
the  temperature  falls  20°  or  more,  and  damp  sultry  air 
under  heavy  clouds  is  exchanged  for  fresh  air  with  bright 
blue  sky.  Then,  as  the  westerly  winds  weaken,  a  southerly 
breeze  springs  up  and  all  these  changes  are  repeated. 


THE  ATMOSPHERE  77 

54.  Winter  Weather  in  the  United  States. — In  winter  the 
succession  of  weather  changes  is  controlled  even  more  dis- 
tinctly than  in  summer  by  the  passage  of  cyclonic  and  anti- 
cyclonic  areas.  A  period  of  fine,  cold,  anticyclonic  weather 
usually  has  a  cloudless  sky  Avith  light  winds.  Tlie  weak  sun- 
shine of  a  short  midwinter  day  cannot  overcome  the  strong 
cooling  by  radiation  during  the  long  clear  night,  and  the  tem- 
perature at  dawn  sinks  to  a  low  degree.  But  as  the  anticy- 
clone moves  eastward  the  pressure  begins  to  fall.  Then  long 
filaments  of  lofty  cirrus  cloud  float  slowly  over  from  the  west, 
announcing  the  approach  of  a  cyclonic  center,  the  wind  turns 
to  a  more  southerly  source,  and  the  temperature  slowly  rises. 

As  the  cyclonic  center  draws  near,  the  wind  strengthens, 
the  sky  is  more  heavily  overcast,  and  the  temperature  rises 
more  distinctly,  for  the  source  of  the  winds  is  now  over 
the  tempered  waters  of  the  sea  on  the  south  and  southeast. 
The  rise  of  temperature  may  continue  steadily  through  the 
night,  so  that  midnight  and  dawn  are  warmer  than  the  pre- 
vious noon ;  for  the  southerly  wind  may  be  more  powerful 
as  a  cause  of  warming  than  the  cloudy  night  is  as  a  cause 
of  cooling.  The  lowering  clouds  let  fall  their  rain  or  snow ; 
if  rain,  the  snow  of  former  storms  is  rapidly  washed  away; 
if  snow,  the  drifts  of  former  storms  are  deepened  and  the 
country  is  shrouded  in  white  far  and  wide.  It  is  under 
the  long-lasting  snow  cover  that  the  "winter  wheat"  of 
the  northern  prairies,  sown  in  November,  is  protected 
from  the  extreme  cold  of  the  winter  winds,  for  the  snow 
is  an  excellent  non-conductor. 

As  the  cyclonic  center  moves  on,  the  northwesterly  winds 
foUow  it  and  the  pressure  rises-     The  rain  or  snow  ceases ; 


78    .  ELEMENTARY  PHYSICAL  GEOGKAPHY 

the  clouds  break  up  and  drift  away  to  the  east  and  reveal  a 
brilliantly  clear  sky.  The  cold  northwesterly  gale  that  has 
come  from  the  far  northern  plains,  west  of  the  cyclonic  cen- 
ter, now  arrives  as  a  "cold  wave."  These  winds  may  be 
from  30°  to  50°  colder  than  the  southerly  winds.  A  fall 
of  temperature  may  thus  be  produced  steadily  through  the 
day,  so  that  noon  is  colder  than  the  previous  midnight. 

If  the  cold  gale  is  accompanied  by  falling  or  drifting 
snow,  it  is  called  a  blizzard,  a  dreaded  storm  on  the  plains 
and  prairies.  As  the  temperature  falls,  furnaces  must  be 
made  hotter  to  keep  houses  warm,  and  destructive  fires  then 
become  more  frequent  than  usual.  The  cold  winds  may 
sweep  far  south,  causing  great  damage  to  southern  crops. 
Then,  as  the  storm  center  moves  eastward,  the  winds  farther 
in  its  rear  weaken;  the  nights  become  calm  and  the  tem- 
perature falls  to  its  lowest  degree,  and  thus  another  spell 
of  fine  and  intensely  cold  weather  is  ushered  in. 

55.  Summer  and  Winter  Weather  in  Temperate  Lati- 
tudes. —  Both  in  winter  and  summer  all  the  changes  here 
described  as  connected  with  areas  of  high  and  of  low 
pressure  are  felt  earlier  in  the  west  than  in  the  east. 
The  eastward  passage  of  cyclonic  or  low-pressure  areas, 
illustrated  in  Figure  30,  is  controlled  by  the  prevailing 
eastward  atmospheric  currents  in  middle  latitudes;  and 
the  direction  of  the  currents  is  determined,  as  has  been 
stated,  by  the  earth's  rotation.  In  summer  time  the 
difference  of  pressure  between  cyclonic  and  anticyclonic 
centers  in  North  America  is  relatively  small  (from  0.5'  to 
0.8  inch);  hence  the  spiraling  winds  are  then  relatively 


THE  ATMOSPHERE 


79 


light.  Moreover,  the  southern  and  northern  regions 
whence  the  inflowing  spiral  winds  are  then  drawn  have 
temperatures  not  greatly  different  (about  85°  and  65°); 
hence  the  changes  of  temperature  are  moderate.  The 
eastward  movement  of   the   cyclonic  areas  is   relatively 


15=  30*" 

Fig.  30.    Storm  Tracks  of  the  North  Temperate  Zone 

slow  (500  miles  a  day  in  the  United  States);  hence  the 
weather  changes  are  gradual. 

All  this  is  changed  in  winter.  The  differences  of  pres- 
sure are  doubled  (from  1.0  to  1.5  inches)  and  the  winds 
often  gain  the  strength  of  gales;  the  regions  whence  the 
southerly  and  northerly  winds  are  drawn  upon  the  Cen- 
tral States  have  very  unlike  temperatures  (80°  and  0°), 


80  ELEMENTARY  PHYSICAL  GEOGRAPHY 

and  the  contrast  between  the  warmth  in  the  front  and 
the  cold  in  the  rear  of  the  cyclonic  areas  is  very  marked. 
In  the  winter  hemisphere  the  general  Winds  are  quick- 
ened, .especially  in  middle  latitudes;  and  therefore  the 
centers  of  high  and  of  low  pressure  drift  eastward  faster 
(800  miles  a  day).  Besides  all  this,  the  cyclonic  and 
anticy clonic  centers  are  more  numerous  in  winter  than 
in  summer ;  hence  weather  changes  in  winter  are  frequent 
as  well  as  rapid  and  strong.  Winter  is  therefore  a  time 
of  stormy  changes  as  well  as  of  low  temperatures,  thus 
resembling  the  conditions  of  the  frigid  zone ;  while  sum- 
mer weather  is  comparatively  even  at  a  high  temperature, 
like  that  of  the  torrid  zone. 

56.  Ocean  Storms.  —  The  stormy  areas  of  the  westerly 
winds  drift  from  North  America  out  upon  the  northern 
Atlantic  ocean,  as  shown  in  Figure  30.  Gales  attend  their 
passage,  especially  in  the  winter  season,  when  a  voyage 
across  this  ocean  is  much  rougher  than  in  summer.  The 
gales  caused  by  these  storms  are  usually  on  the  southern 
side  of  the  low-pressure  center,  and  hence  from  a  western 
quarter.  The  general  course  of  the  storm  centers  is  north- 
eastward, so  that  a  cyclonic  center  that  passes  over  New 
England  or  down  the  St.  Lawrence  valley  is  more  likely 
to  affect  the  weather  of  Norway  than  that  of  Spain. 
Storms  from  the  North  Pacific  ocean  come  upon  the  wesi> 
em  coast  of  North  America;  they  may  before  breaking  up 
pass  far  inland  or  even  cross  the  whole  breadth  of  the  con- 
tinent. The  storms  in  the  prevailing  westerly  winds  of 
the  southern  hemisphere  encounter  but  little  land  in  their 


THE  ATMOSPHERE  81 

course.  They  are  more  severe  in  the  southern  winter 
(June  to  August)  than  in  the  summer  (December  to  Feb- 
ruary). South  America  reaches  farther  south  than  the 
other  continents;  hence  vessels  rounding  Cape  Horn  must 
enter  much  farther  into  this  stormy  belt  than  in  rounding 
the  Cape  of  Good  Hope,  and  the  passage  around  Cape 
Horn  is  dreaded  for  this  reason. 

57.  Cyclonic  Winds. — The  inflowing  spiral  winds  of 
cyclonic  storms  are  often  given  special  names  in  different 
parts  of  the  world,  according  to  the  kind  of  weather  they 
may  bring.  The  cold  wave  of  our  winters,  sweeping  over 
the  central  and  eastern  United  States  from  the  far  northern 
plains  in  the  rear  of  cyclonic  centers,  has  already  been 
described.  In  western  Europe  the  cold  wind  of  winter  is 
the  northeaster,  because  the  plains  of  northeastern  Europe 
supply  colder  air  than  the  ocean  about  Iceland.  It  occurs 
when  a  cyclonic  center  follows  a  more  southerly  track  than 
usual.  The  blizzard  of  our  plains  corresponds  to  the 
buran  of  Siberia.  No  special  name  has  been  given  in  the 
United  States  to  the  sultry  southerly  wind  that  frequently 
brings  unseasonably  warm  weather  in  front  of  a  cyclonic 
center.  It  might  be  called  a  sirocco,  after  the  Italian  name 
of  a  similar  wind.  In  the  southern  hemisphere  cold  winds 
come  from  the  south,  and  hot  winds  from  the  north.  In 
southern  Australia  the  wind  that  corresponds  to  the  sirocco 
is  called  a  brickfielder,  because  it  bakes  the  fields  hard 
and  dry. 

58.  Weather  Predictions.  —  Weather  maps  from  which 
the  general  character  of  the  weather  for  one  or  two  days 


82     ELEMENTARY  PHYSICAL  GEOGRAPHY 

may  be  predicted  are  now  prepared  daily  in  many  countries. 
Observations  of  the  weather  made  at  the  same  hour  at 
many  different  places  are  telegraphed  to  the  central  station, 
—  the  Weather  Bureau  at  Washington  for  the  United 
States.  They  are  then  promptly  charted  so  that  the  areas 
of  high  and  low  pressure,  the  temperature,  the  direction 
and  strength  of  the  winds,  the  distribution  of  clear  and 
cloudy  sky  and  of  rain  or  snow  are  all  shown.  It  is  known, 
as  described  on  preceding  pages,  that  cyclonic  and  anti- 
cyclonic  areas  with  their  attending  weather  conditions  usu- 
ally move  eastward ;  it  is  therefore  possible  to  foretell  with 
considerable  accuracy  the  weather  that  may  be  expected 
for  a  day  or  two  in  various  parts  of  the  country  from  the 
conditions  shown  on  the  weather  map. 

Predi<?tions  thus  prepared  are  distributed  by  telegraph, 
and  published  in  special  bulletins  and  in  newspapers  for 
the  benefit  of  the  public. 

No  one  has  yet  succeeded  in  making  successful  predic- 
tions of  the  weather  regularly  for  definite  districts  several 
weeks  or  months  in  advance.  It  is  true  that  such  "  long- 
range  predictions,"  as  they  are  called,  are  frequently  pub- 
lished. As  the  weather  differs  in  different  parts  of  the 
country,  predictions  of  hot  weather  over  the  central  United 
States  in  July  and  of  cold  weather  in  January,  or  rain  in 
March  and  drought  in  September,  may  be  correct  for  one 
place  or  another,  but  they  must  be  incorrect  for  other 
places.     Such  predictions  cannot  be  depended  upon. 

59.  Climate.  —  The  general  succession  of  weather 
changes    through   the    year,    averaged   for   many   years, 


THE  ATMOSPHERE  83 

constitutes  the  climate  of  a  region.  The  five  climatic 
zones  into  which  the  earth  is  commonly  divided  need 
further  subdivision  in  order  to  correspond  to  the  many 
well-marked  types  of  climate  on  lands  and  seas,  on  coasts 
and  inland  regions,  on  lowlands  and  highlands. 

The  trade-wind  belt  at  sea  has  the  simplest  climate  in 
the  world,  with  small  daily  and  yearly  changes  of  tempera- 
ture. The  steady  wind  and  fair  weather  of  almost  any 
day  give  a  fair  sample  of  the  year.  Low  lands  under 
the  regular  trade  winds  suffer  greater  daily  and  yearly 
changes  of  temperature,  with  light  rainfall. 

Compare  the  mean  annual  range  of  temperature  in  the  West 
Indies  and  in  inner  Africa,  latitude  20°  N.,  Figure  20 ;  in  Africa, 
Indian  ocean,  and  Australia,  latitude  20°  S. 

The  subequatorial  belt  has  a  distinct  seasonal  change 
as  the  clouds  of  the  heat  equator  move  away  and  give 
place  to  the  dry  trade  winds.  The  Sudan,  between  the 
desert  of  Sahara  and  the  forest  belt  of  equatorial  Africa, 
has  plentiful  rainfall  and  active  plant  growth  when  the 
equatorial  cloud  belt  moves  north,  bringing  the  wet  sea- 
son (May  to  August),  but  it  becomes  parched,  barren,  and 
dusty  under  the  trade  winds  of  the  dry  season  (December 
to  March). 

Examine  Figure  21  and  state  in  what  months  you  would  expect 
rain  on  or  near  the  geographical  equator.  At  the  head  of  the  Gulf 
of  Guinea,  west  equatorial  Africa,  rain  is  most  abundant  in  March 
and  October  to  November.  In  Ceylon  the  rainfall  is  greater  in  May 
and  October  than  in  the  other  months;  at  the  city  of  Quito,  Ecua- 
dor, in  April  and  November.  How  do  you  explain  these  double 
rainy  seasons? 


84  ELEMENTARY  PHYSICAL  GEOGRAPHY 

The  south  temperate  zone  is  mostly  an  oceanic  belt. 
The  changes  of  air  temperature  with  the  seasons  are  small, 
as  shown  in  Figure  20,  because  the  water  surface  warms 
and  cools  so  little  in  summer  and  winter.  Its  winds  are 
more  stormy  in  winter,  less  stormy  in  summer ;  nevei" 
very  hot  or  extremely  cold,  but  for  the  most  part  chill, 
damp,  and  blustering.  Islands  near  50°  S.  are  hardly 
habitable,  not  that  the  winters  are  too  severe,  although 
cloudy  and  wet,  but  that  the  summers  are  too  chilling. 

The  north  temperate  zone  contains  large  areas  of  both 
land  and  water,  and  the  temperatures  of  its  various  parts 
are  therefore  very  unlike,  as  shown  in  Figures  18,  19,  and 
20.  The  parallel  of  50°  N.  crosses  regions  whose  climates 
are  so  different  that  they  would  hardly  have  been  placed 
under  a  single  zone  had  they  been  studied  before  being 
named ;  but  the  name  was  given  from  the  truly  temper- 
ate climate  of  southern  Europe,  before  other  parts  of  the 
world  were  well  known. 

Beginning  in  the  moderate  climate  of  the  North  Atlantic, 
Figure  20,  the  parallel  of  50°  N.  enters  the  favorable 
climate  of  middle  Europe,  where  the  last  thousand  years 
have  witnessed  the  greatest  human  progress  in  the  arts 
and  sciences  that  the  world  has  ever  known.  It  crosses 
the  broad  deserts  of  central  Asia,  where  the  scattered 
population  is  held  down  in  barbarism  chiefly  by  severe 
and  unfavorable  climatic  conditions. 

The  broad  North  Pacific  has  in  this  latitude  a  climate 
as  moderate  as  that  of  the  North  Atlantic.  Passing  the 
tempered  and  moist  climate  of  the  coast  belt  of  British 
Columbia,  and  crossing  the  snowy  mountain  ranges  beyond, 


THE  ATMOSPHERE 


85 


the  severe  interior  climate  of  middle  Canada  is  reached, 
with  extremes  of  temperature,  summer  and  winter,  only 
less  than  those  of  inner  Asia.  As  far  as  habitability  is 
concerned,  the  middle  north  temperate  zone  contains 
climatic  differences  almost  as  great  as  those  found  in 
passing  from  the  equator  to  the  pole. 

Compare  this  account  of  the  climate  of  latitude  50°  N.  with  the 
conditions  in  latitude  50°  S. 


Supplement  to  Chapter  II 

60.  Deflection  of  Winds  by  the  Earth's  Rotation. —  Place  a  marble 
in  the  center  of  a  circular  board.  Set  the  marble  in  motion  by 
striking  it  a  light  blow.  It  will  move 
in  a  straight  line  along  a  radius  from 
center  to  circumference.  Now  let  the 
board  be  given  a  slow  movement  of 
rotation  around  a  pivot  at  its  center. 
The  marble  will  now  again  move 
directly  outward,  but  the  line  that  it 
traces  on  the  turning  board  will  be 
curved  so  as  to  fall  behind  the  radius 
on  which  it  started.  If  the  board 
turns  to  the  left,  the  marble  will  be 
deflected  to  the  right  of  its  original 
path ;  if  the  board  turns  rapidly,  the 
deflection  will  be  strong. 

In  Figure  31  the  circle,  A,  resting 
on  the  earth  in  a  northern  latitude 
may  be  taken  to  represent  a  circular 
board  or  surface  of  great  size.      A 

north  line  drawn  from  the  center  of  the  circle  meets  the  prolonged 
axis  of  the  earth  at  N.  When  the  rotation  of  the  earth  has  car- 
ried the  circle  to  B  the  same  north  line  has  a  new  direction,  BN^ 


Fig.  31. 


Rotation  of  a  Disk  on  a 
Rotating  Globe 


86     ELEMENTARY  PHYSICAL  GEOGRAPHY 

showing  that  the  circle  has  turned  somewhat  to  the  left  with  respect 
to  its  own  center.  Hence  any  such  circle  may  be  taken  to  represent 
a  turning  surface.  A  body  beginning  to  move  in  any  direction  from 
the  point  A  will  tend  to  turn  to  the  right,  because  of  the  rotation  of 
the  circle  to  the  left.  This  tendency  will  be  strongest  at  the  pole, 
because  a  circle  there  rotates  with  the  greatest  rapidity,  turning 
completely  round  in  twenty-four  hours.  The  tendency  is  zero  at  the 
equator,  because  there  a  circle  has  no  movement  of  rotation  with 
respect  to  its  own  center.  In  the  southern  hemisphere,  where  the 
circle  must  turn  to  the  right,  the  deflective  force  acts  to  the  left. 

The  wind  is  so  free  to  move  over  the  earth's  surface  that  it  is 
greatly  affected  by  the  deflective  force  arising  from  the  earth's  rota- 
tion. Hence  the  members  of  the  atmospheric  circulation  do  not  flow 
north  and  south,  but  are  always  deflected  to  the  right  of  these  direc- 
tions in  the  northern  hemisphere,  and  to  the  left  in  the  southern. 

The  lofty  overflow  currents  are  deflected  so  as  to  run  from  the 
southwest  or  even  from  the  west-southwest  in  the  northern  hemi- 
sphere, from  the  northwest  or  west-northwest  in  the  southern.  The 
winds  approaching  the  equator  do  not  blow  directly  from  the  north 
and  the  south  in  the  two  hemispheres,  but  are  deflected  so  as  to  blow 
from  the  northeast  and  southeast,  forming  the  trade  winds.  The 
whirling  winds  of  cyclonic  storms,  described  on  pages  45  and  67, 
attempt  to  blow  toward  their  centers  of  low  pressure,  but  on  account 
of  the  earth's  rotation  the  winds  are  deflected  to  the  right  in  the 
northern  hemisphere,  and  to  the  left  in  the  southern ;  thus  the  storms 
are  given  their  whirling  movement. 

It  should  be  noted  that  winds  will  be  deflected  to  the  right  or  left, 
in  whatever  direction  they  begin  to  blow,  east  and  west  winds  being 
affected  just  as  much  as  north  and  south  winds.  Ocean  currents  are 
similarly  affected  but  to  a  less  degree,  because  they  move  more 
slowly  than  the  winds.  Rivers  tend  to  turn  to  the  right  in  the 
northern  hemisphere  and  to  the  left  in  the  southern;  but  the 
tendency  is  practically  overcome  by  the  resistance  of  the  banks. 
Similarly  a  railroad  train  tends  to  be  deflected,  but  is  held  to  its 
track  by  the  flanges  on  the  wheels. 


THE  ATMOSPHERE  87 

61.   Practical  Method  of  studying  Observations  of  the  Sun.  —  In 

studying  the  control  of  the  seasons  by  the  sun  it  is  desirable  to 
determine  the  length  of  the  day  and  the  midday  altitude  of  the  sun 
by  observations  about  once  a  fortnight,  or  at  least  once  a  month, 
through  the  school  year,  with  additional  observations  near  the  times 
of  shortest  and  longest  days  or  of  lowest  and  highest  midday  sun. 

If  sunrise  comes  at  too  early  an  hour  for  convenient  observation, 
note  that  midday  occurs  at  the  middle  of  the  interval  between  sun- 
rise and  sunset.  Midday  is  determined  by  the  method  explained  on 
page  8.  The  time  of  sunset  may  be  directly  observed.  The  time 
of  sunrise  may  then  be  determined  by  counting  back  as  many  hours 
and  minutes  before  midday  as  sunset  occurs  after  midday. 

The  midday  altitude  of  the  sun  may  be  determined  as  follows : 
Use  such  a  box  as  is  shown  in  Figure  3,  and  drive  a  pin  square  into 
one  side  of  the  box,  close  to  its  upper  corner.  With  the  pin  as  a  cen- 
ter, draw  an  arc  of  a  circle  on  the  box  side.  Draw  a  horizontal  and 
a  vertical  line  from  the  pin  to  the  arc.  The  arc  included  between  the 
two  lines  will  be  a  right  angle,  or  90°.  Divide  it  into  halves,  divide 
the  halves  into  thirds,  and  the  thirds  again  into  thirds.  The  small 
divisions  thus  found  will  be  5°  of  arc.  ]N"umber  the  divisions  from 
0  at  the  horizontal  line  to  90°  at  the  vertical. 

As  the  sun  approaches  the  meridian,  turn  the  side  of  the  box  so 
that  it  is  directed  toward  the  sun.  The  shadow  of  the  pin  is  then 
seen  as  a  slanting  line,  and  the  altitude  of  the  sun  is  indicated  by 
the  angle  that  the  shadow  line  makes  with  the  horizontal  line.  Con- 
tinue to  turn  the  box  after  the  sun,  until  the  altitude  indicated  by 
the  shadow  line  begins  to  decrease.  The  greatest  angle  thus  found 
is  the  midday  altitude  of  the  sun. 

In  Figure  32  let  the  horizontal  scale  represent  the  days  of  the 
year,  and  the  vertical  scale  the  angular  altitude  of  the  sun  at  mid- 
day. Mark  the  sun's  midday  altitude  by  dots  opposite  the  appro- 
priate dates.  At  the  close  of  the  school  year  draw  a  curve  through 
the  dots.  Draw  lines  parallel  to  the  base  line  and  touching  the 
upper  and  lower  points  of  the  curves.  Draw  a  third  line  midway 
between  the  last  two. 


88      ELEMENTARY  PHYSICAL  GEOGRAPHY 

In  Figure  33  the  vertical  scale  represents  the  days  of  the  year ; 
the  horizontal  scale  measures  hours  before  and  after  midday.  Mark 
dots  to  the  right  and  left  of  the  midday  line  and  opposite  to  the 
appropriate  dates,  to  represent  the  time  before  and  after  midday  at 
which  sunrise  and  sunset  occur.  Connect  these  dots  by  curved  lines. 
Draw  two  lines  that  shall  stand  six  hours  on  either  side  of  the  mid- 
day line. 

Now  determine  from  Figure  32  the  dates  when  the  sun  has  the 
greatest  midday  altitude  (or  when  it  stands  farthest  north  in  the  sky) 
when  it  has  the  least  midday  altitude  (farthest  south  in  the  sky), 


?ept.  ,  Oct.   ,  Nov.  ,  Dec.  ,  Jan.  ,  Feb.  ,  Mar.  ,  Apr.  ,  May  ,  June  , 
Fia.  32.    Diagram  of  the  Sun's  Midday  Altitude 

and.  the  two  dates  when  its  altitude  is  that  of  the  mid-horizontal 
line.  Determine  from  Figure  33  the  date  when  the  day  is  longest, 
when  it  is  shortest,  and  the  two  dates  when  it  is  twelve  hours  long. 
Compare  the  dates  thus  found.  If  the  observations  are  well  made 
and  the  diagrams  accurately  constructed,  the  four  dates  should  agree 
on  the  two  diagrams. 

The  dates  when  the  days  are  twelve  hours  long,  and  therefore 
equal  to  the  nights,  are  March  21  and  September  22  ;  these  dates 
are  called  the  vernal  (spring)  and  autumnal  (fall)  equinox  (equal- 
night).  The  date  when  the  sun  is  farthest  north,  and  when  the  day 
in  the  northern  hemisphere  is  consequently  longest,  is  June  21. 
This  is  called  the  summer  solstice  (sun-stand),  because  the  sun,  hav- 
ing then  finished  its  northward  movement,  stops  or  "stands"  before 
beginning   its   southward  movement.     The   day  when   the   sun  is 


THE  ATMOSPHERE 


89 


farthest  south,  dnd  when  the  day  is  consequently  shortest  in  the 
northern  hemisphere,  is  called  the  winter  solstice;  this  date  is 
December  21. 

Between  what  dates  is  the  sun  moving  northward  in  the  sky? 
Between  what  dates  is  it  moving  southward  ?  Between  what  dates 
are  the  days  lengthening? 


12 


6 


M 


12 


8e?t. 


0:t 


Dic. 


At  the  time  of  the  equi- 
noxes the  sun  must  be  on 
the  equator  of  the  sky ;  for, 
as  is  shown  in  Figure  17, 
it  is  only  then  that  equal 
days  and  nights  occur  in  all 
parts  of  the  world.  Hence 
the  middle  horizontal  line 
in  Figure  32  must  repre- 
sent the  angular  altitude 
of  the  sky  equator  where  it 
crosses  the  meridian.  The 
angular  distance  of  the  sun 
north  or  south  of  the  sky 
equator  for  any  day  of  the 
year  may  be  measured  by 
the  scale  at  the  side  of 
the  figure.  The  greatest 
angular  distance  of  the  sun 
from  the  sky  equator  gives 
means  of  determining  the  yiq   33. 

limits  of  the  zones.     (See 
page  48.) 

How  far  north  of  the  sky  equator  does  the  sun  stand  at  the  time  of 
the  summer  solstice  ?  How  far  south  at  the  time  of  the  winter  solstice  ? 
Ho.w  many  days  is  it  north  of  the  sky  equator?  How  many  days  south  ? 

62.  Determination  of  Latitude.  —  The  sky  equator  passes  overhead 
(in  the  zenith)  to  an  observer  at  the  earth's  equator ;  hence  the  sky 
equator  will  depart  one  degree  from  the  zenith  for  every  degree  that 


A:)r. 


Miy 


Diagram  of  Sunrise  and 
Sunset  Hours 


90  ELEMENTARY  PHYSICAL  GEOGRAPHY 

the  observer  moves  toward  the  pole.  Therefore  the  latitude  of  a 
place  must  equal  the  angular  distance  of  the  sky  equator  from  the 
zenith.  Latitude  may  thus  be  determined  on  any  day  by  measuring 
the  sun's  midday  altitude  and  allowing  for  its  distance  from  the  sky 
equator,  as  determined  by  Figure  32.  The  altitude  of  the  sky  equa- 
tor subtracted  from  90°  is  the  latitude.  Results  that  are  correct 
within  a  few  degrees  may  be  obtained  even  by  the  rough  obser- 
vations here  described. 

If  records  of  the  kind  indicated  above  are  taken  on  different  dates 
in  successive  years,  the  increasing  number  of  dots  will  give  better  and 
better  definition  of  the  curves  in  Figures  32  and  33 ;  but  minute 
accuracy  of  performance  is  not  so  important  as  intelligent  exercise  in 
the  application  of  principles. 

Examples.  If  the  midday  altitude  of  the  sun  is  50°  on  the  22d  of 
September,  what  is  the  latitude  of  the  place  of  observation  ?  What 
would  the  latitude  be  if  the  observation  had  been  made  on  Decem- 
ber 21  ?  on  March  21  ?  on  June  21  ? 

63.  Exercises  on  Weather  MaJ)s.  —  Many  instructive  exercises 
may  be  based  on  the  daily  weather  maps.  Copies  of  these  maps  for 
school  use  may  be  obtained,  under  certain  conditions,  by  addressing 
the  Chief  of  the  Weather  Bureau,  Washington,  D.C.  The  exercises 
here  described  may  be  performed  on  the  original  maps,  or  on  outline 
maps  of  the  United  States  upon  which  certain  weather  elements  are 
copied.  It  is  usually  best  to  select  maps  on  which  differences  of 
pressure  are  well  defined,  in  order  to  exhibit  strongly  marked  types 
•of  weather. 

64.  Distribution  of  Pressure. — Plat  upon  a  blank  map  of  the 
United  States  the  barometer  readings  taken  from  a  weather  map, 
and  thus  guided  draw  in  lines  of  equal  pressure,  or  isobars,  for  every 
tenth  of  an  inch  according  to  the  method  already  explained  for  iso- 
therms. The  difference  of  pressure  between  the  highest  and  lowest 
readings  is  often  six  or  eight  tenths  of  an  inch  or  more.  Shade  the 
areas  of  high  and  low  pressure,  leaving  the  area  of  intermediate  pres- 
sure (for  example,  from  29.9  to  30.1  inches)  blank.     Describe  the 


THE  ATMOSPHERE  91 

distribution  of  pressure  thus  shown.  Draw  a  similar  map  for  the 
next  day.  Describe  the  change  in  the  distribution  of  pressure  thus 
found.     Temperature  may  be  similarly  treated. 

65.  Movement  of  Winds  in  Areas  of  High  and  Low  Pressure. — 
Select  several  well-defined  examples  of  high-  and  low-pressure  areas 
whose  centers  lie  in  the  mid-Ohio  valley,  so  that  observations  are 
provided  on  all  sides  of  them.  Plat  the  wind  arrows  (the  arrow 
flies  with  the  wind  on  weather  maps),  and  let  their  length  indicate 
wind  velocity  (an  eighth  of  an  inch  for  five  or  ten  miles) .  Draw  addi- 
tional lines  to  represent  inferred  wind  movement  between  the  points 
of  observation.  How  is  the  direction  of  the  wind  at  any  place 
related  to  the  distribution  of  pressure  about  that  place  ?  In  answer- 
ing this  question  it  will  be  well  to  draw,  through  the  point  consid- 
ered, a  line  at  right  angles  to  the  neighboring  isobars.  This  line 
shows  the  direction  of  increase  or  decrease  of  pressure.  Describe 
the  general  movement  of  the  winds  (direction  and  velocity)  with 
respect  to  a  center  of  high  pressure  ;  of  low  pressure. 

66.  Composite  Portrait  of  High-  and  Low-Pressure  Areas.  —  Rule 
a  straight  line  through  the  center  of  a  sheet  of  tracing  paper  and  mark 
the  ends  of  the  line  N  and  S.  Lay  the  center  of  the  sheet  over  the 
center  of  an  area  of  low  pressure  and  turn  the  N-S  line  so  that  it 
shall  lie  most  nearly  parallel  to  the  adjacent  meridians.  Trace  off 
the  signs  indicating  the  state  of  the  sky  (clear,  fair,  rain,  or  snow)  at 
various  stations.  Do  the  same  for  several  other  maps  that  have  a 
low-pressure  center.  Do  the  same  on  another  tracing  paper  for  sev- 
eral areas  of  high  pressure.  Compare  the  results  as  to  the  distribu- 
tion and  frequency  of  clear,  fair,  and  wet  weather,  with  respect  to 
centers  of  high  and  of  low  pressure.  Winds  may  be  similarly 
treated. 

67.  Progression  of  High-  and  Low-Pressure  Areas.  —  Select  a  series 
of  four  or  five  maps  on  which  a  well-defined  area  of  high  or 
of  low  pressure  is  represented  as  occupying  successive  positions 
eastward  across  the  country  from  the  Rocky  mountains  to  the 
Atlantic.     Chart  on  an  outline  map  the  path  of  the  center  of  the 


92      ELEMENTARY  PHYSICAL  GEOGRAPHY 

area  studied  and  determine  its  velocity  in  miles  an  hour  and  a  day. 
Note  the  weather  changes  (pressure,  temperature,  wind,  sky)  that 
occur  at  a  single  station  as  the  cyclonic  or  anticyclonic  area  passes 
over  it.  What  is  the  general  character  of  these  changes  for  a  cyclonic 
area  ?  for  an  anticyclonic  area  ? 

Compare  the  succession  of  weather  changes  at  any  place,  as  deter- 
mined from  weather  maps,  with  the  weather  changes  observed  at 
school  dui-ing  several  days.  How  are  the  local  weather  changes 
related  to  passing  areas  of  high  or  of  low  pressure  (anticyclonic  and 
cyclonic  areas)  ? 

QUESTIONS 

Sec.  19.  What  processes  depend  on  the  atmosphere?  What  is 
known  of  its  height? 

20.  What  is  the  composition  of  air?  How  is  oxygen  used? 
carbonic  dioxide? 

21.  What  is  the  pressure  of  the  atmosphere  on  a  square  foot  of 
surface  ?  Describe  the  mercurial  barometer ;  the  aneroid  barometer. 
How  can  barometers  be  used  to  measure  mountain  heights  ? 

22.  How  does  the  density  of  the  air  vary ?  Why?  What  is  the 
weight  of  a  cubic  foot  of  air  at  sea  level  ?     How  is  sound  carried  ? 

23.  How  are  the  colors  of  the  sky  produced  ?  What  is  the  twi- 
light arch  ?     When  may  it  be  seen  ? 

24.  How  is  the  temperature  of  the  air  controlled?  Why  is  the 
upper  air  cold?  Consider  the  diurnal  range  of  temperature  in  the 
upper  and  lower  air.  How  do  the  processes  of  absorption,  conduc- 
tion, and  radiation  affect  the  temperature  of  the  air  ?  How  does  the 
form  of  the  earth  affect  the  distribution  of  temperature?  How  is 
the  weight  of  air  affected  by  heat  ? 

25.  What  is  a  mirage?  How  is  it  produced  on  level  deserts? 
on  a  water  surface? 

26.  Explain  the  construction  of  a  thermometer.  How  do  the 
Fahrenheit  and  Centigrade  thermometer  scales  differ?     What  is  a 


THE   ATMOSPHERE  93 

thermograph?   a  maximum   thermometer?   a  minimum   thermom- 
eter?   How  should  a  thermometer  be  exposed? 

27.  How  are  temperature  charts  constructed?  What  is  an  iso- 
thermal line?  How  are  mean  temperatures  determined?  What 
is  the  heat  equator?  Describe  its  position.  Compare  the  mean 
annual  isotherms  of  the  northern  and  southern  hemispheres. 

28.  Describe  the  movements  of  the  air  between  a  hot  and  a  cold 
room.  What  is  a  convectional  circulation?  Describe  the  general 
circulation  of  the  atmosphere  between  equator  and  poles.  What 
changes  of  temperature  are  caused  in  ascending  and  descending 
currents  ?     What  is  the  planetary  circulation  ? 

29.  How  are  winds  named?  How  is  their  strength  described? 
What  is  an  anemometer? 

30.  Describe  the  steps  in  the  circulation  of  water  through  the 
atmosphere.     How  is  rain  caused? 

31.  What  are  the  chief  members  of  the  planetary  winds? 
Describe  the  trade  winds.  Where  do  they  occur?  What  is  their 
direction?  What  is  the  relation  of  rainfall  and  deserts  to  the 
trade  winds  ?  of  wet  and  dry  mountain  slopes  to  the  trade  winds  ? 
Give  examples.  Describe  the  prevailing  westerlies.  Where  do  they 
occur  ?  What  is  their  direction  ?  How  is  rainfall  related  to  these 
winds?  What  are  the  doldrums?  the  horse  latitudes?  Describe 
and  explain  the  weather  of  the  doldrums;  of  the  horse  latitudes. 

32.  Describe  the  whirls  of  the  westerly  winds.  Explain  their 
weather.  How  fast  do  they  travel?  Compare  the  whirls  of  the 
two  hemispheres.  Compare  the  atmospheric  pressure  at  the  center 
of  the  inward  and  outward  whirls.  What  names  are  given  to  these 
whirls  ? 

33.  Describe  the  movement  of  the  earth  around  the  sun.  Com- 
pare the  attitudes  of  the  northern  and  southern  hemispheres  with 
respect  to  the  sun  in  the  two  half  years.  What  are  the  resulting 
variations  of  temperature  ?  What  are  the  months  of  each  of  the  f  our 
seasons  in  the  northern  hemisphere  ?  in  the  southern  ?  What  are  the 
limits  of  the  torrid  zone  ?  the  frigid  zones  ?  the  temperate  zones  ? 


94     ELEMENTARY  PHYSICAL  GEOGRAPHY 

34.  What  are  the  apparent  movements  of  the  sun  in  December? 
in  June  ?  How  are  the  temperatures  of  winter  and  summer  related 
to  these  movements?  Explain  the  rising  temperature  of  spring; 
the  falling  temperature  of  autumn. 

35,  36.  How  may  the  change  of  seasons  be  described  if  the  earth 
as  a  whole  is  considered  ?  Mention  the  most  striking  facts  shown  on 
the  isothermal  charts  for  January  and  for  July. 

37.  Describe  the  most  striking  facts  shown  on  the  chart  of  mean 
annual  temperature  range.  Compare  the  annual  range  of  temperature 
over  the  northern  continents  and  the  southern  oceans  ;  on  western  and 
eastern  coasts  in  temperate  latitudes.  Why  are  the  annual  changes 
large  in  the  northern  hemisphere  ?     Why  small  in  the  southern  ? 

38.  How  do  the  terrestrial  winds  differ  from  the  planetary? 
Explain  the  differences.  Describe  and  explain  the  subtropical 
belts.  Name  some  coimtries  lying  in  a  subtropical  belt  and  describe 
them  as  to  winds  and  rainfall.  Describe  and  explain  the  subequa- 
torial  belt.  Describe  its  migration,  Figures  22,  23,  on  the  Atlantic 
ocean;  on  the  eastern  Pacific;  on  the  Indian  ocean.  Give  some 
examples  of  subequatorial  rainfall  in  South  America ;  in  Africa. 

39.  What  are  monsoons?  How  are  they  caused ?  Where  do  they 
occur,  Figures  22,  23  ?     Describe  the  monsoons  of  the  Indian  ocean. 

40.  41,  42.  How  do  the  continents  affect  the  terrestrial  winds? 
Give  examples  from  Asia.  What  are  land  and  sea  breezes?  How 
do  fair-weather  winds  on  lands  vary  from  night  to  day?  Explain 
this  variation.     Why  does  it  not  occur  at  sea  ? 

43.  What  is  humidity?  How  does  it  vary  with  temperature? 
What  is  saturation?     Compare  the  feeling  of  damp  and  dry  air. 

44.  What  is  the  dew-point  ?  How  may  it  be  determined  ?  What 
are  dew  and  frost  ?     Under  what  conditions  are  they  produced  ? 

45.  Describe  the  chief  kinds  of  clouds:  cumulus,  cirrus,  cirro- 
stratus,    alto-nimbus,   and   nimbus.      Describe    a    halo ;    a   corona. 

46.  47,  48.  Describe  a  thunderstorm.  Where  and  when  do  such 
storms  occur?  What  can  you  say  about  lightning  and  thunder? 
What  is  a  cloud-burst  ?  a  rainbow  ?  a  tornado  ?  a  waterspout  ? 


THE  ATMOSPHERE  95 

49.  Where  and  how  are  tropical  cyclones  formed  ?  How  do  their 
winds  blow  ?  How  do  these  storms  travel  ?  In  what  regions  do  they 
occur?  In  what  months?  Why  are  there  two  seasons  of  cyclones 
in  the  northern  Indian  ocean?  Why  are  tropical  cyclones  not 
formed  in  the  South  Atlantic? 

50.  What  is  meant  by  rainfall?  Describe  and  explain  snow ;  rain  ; 
hail ;  frozen  rain.  How  is  rainfall  measured  ?  State  the  relation  of 
rainfall  to  agriculture.  Give  several  examples  of  the  relation  between 
the  terrestrial  winds,  Figures  22,  23,  and  rainfall.  Figure  28.  Where 
is  the  heaviest  rainfall  of  the  world ?  What  is  its  amount?  its  cause ? 
Why  is  the  rainfall  of  low  latitudes  large,  and  of  hi^h  latitudes  small  ? 

51.  Describe  the  rainfall  of  the  Pacific  slope  of  the  United  States  ; 
of  the  interior  region ;  of  the  eastern  region. 

52.  What  is  meant  by  weather  ?  Describe  the  prevailing  weather  of 
the  torrid  zone ;  of  the  temperate  zones  in  summer ;  in  winter ;  of 
frigid  latitudes.    Explain  the  effects  of  cyclonic  and  anticyclonic  areas. 

53.  Describe  a  period  of  summer  weather  in  the  eastern  United 
States  as  a  cyclonic  area  is  approaching ;  after  it  has  passed.  When 
are  sunstrokes  and  thunderstorms  most  common  ? 

54.  Describe  our  winter  weather  in  front  of  a  cyclonic  area ;  in 
the  rear.  When  may  a  warming  night  occur?  a  cooling  day? 
What  is  a  cold  wave?   a  blizzard? 

55.  Describe  the  tracks  of  high-  and  low-pressure  areas  in  the 
north  temperate  zone.  What  changes  of  pressure  do  they  cause 
in  summer?  in  winter?  How  fast  do  they  travel  in  summer?  in 
winter?  Compare  the  changes  of  temperature  that  they  produce 
in  the  central  part  of  United  States  in  summer  and  in  winter. 

56.  57,  58.  Describe  the  storms  of  the  North  Atlantic.  What  is 
a  buran?  a  sirocco?  a  brickfielder?    How  is  the  weather  predicted? 

59.  What  is  climate?  Describe  the  climate  of  the  trade-wind 
belt  at  sea ;  of  the  subequatorial  belt ;  of  the  south  temperate  zone  ; 
of  the  north  temperate  zone  on  the  oceans ;  on  the  lands.  Describe 
the  climates  of  latitude  50°  N. ;  of  latitude  50"  S. 


CHAPTER   III 
THE   OCEAN 

68.  Form  of  the  Ocean.  —  The  ocean  is  a  sheet  of  salt 
water,  clear  and  blue,  covering  about  three  quarters  of  the 
earth's  surface  "*to  an  average  depth  of  about  two  miles. 
It  lies  in  broad  depressions  or  basins  between  the  conti- 
nents, its  shallow  edges  lapping  over  the  margin  of  the 
continental  masses. 

The  outline  and  distribution  of  the  ocean  are  best 
studied  on  a  globe.  A  vast  water  area,  comprising  the 
Pacific  and  Antarctic  oceans,  covei-s  nearly  half  the  earth. 
The  water  surface  is  broken  only  by  Australia,  the  Antarc- 
tic lands,  and  many  small  islands.  A  short  Indian  arm 
extends  from  this  great  oceanic  area  into  the  space  between 
Africa  and  Australia,  and  a  long,  relatively  narrow  Atlan- 
tic arm  runs  between  the  Old  and  New  Worlds,  ending  in 
the  gulf-like  Arctic  ocean  around  the  north  pole. 

The  surface  of  a  hemisphere  whose  pole  is  near  New 
Zealand  is  nearly  all  water,  as  in  Figure  34 ;  while  the 
opposite  hemisphere  contains  all  the  large  land  areas, 
except  Australia,  the  Antarctic  lands,  and  the  extremity 
of  South  America.  It  is  not  a  little  curious  to  note  that 
near  the  pole  of  the  land  hemisphere  stands  the  greatest 
city  of  the  world,  the  capital  of  the  empire  whose  colonies 
are  more  widely  spread  than  those  of  any  other  nation. 

96 


THE  OCEAN 


97 


What  lands  lie  entirely  in  the  land  hemisphere?  What  oceans 
lie  largely  in  the  land  hemisphere?  Trace  the  course  of  the  gi*eat 
circle  which  divides  the  land  and  water  hemispheres. 

69.  The  Ocean  as  a  Highway. —  The  lands  are  widely 
separated  by  the  oceans,  and  navigation  of  the  "high  seas" 
requires  great  skill  and  is  fraught  with  many  dangers. 
But  the  oceans  are  a  ready-made  highway,  where  movement 


t^r^r^^^ 


Fio.  34.    Water  and  Land  Hemispheres 

is  easy  and  open  to  all  comers ;  the  winds  furnish  free  motive 
power  to  sailing  vessels,  and  coal  is  an  economical  fuel  for 
steamers.  Hence  ocean-going  vessels  are  used  to  carry 
large  quantities  of  merchandise  from  one  part  of  the  world 
to  another. 

Before  railroads  were  invented  the  two  sides  of  the  North 
Atlantic  were  in  more  active  communication  by  sea  than  the 
two  sides  of  any  continent  overland.  Since  railroads  have 
been  extensively  built  inland  transportation  has  greatly  in- 
creased ;  but  a  great  part  of  international  commerce  is  still 
carried  on  across  the  oceans  in  steamships  and  sailing  vessels. 


98 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


70.  Exploration  of  the  Ocean. — The  earlier  exploration 
of  the  ocean  discovered  its  shore  lines  on  the  continents  and 
islands.  Exploration  in  the  latter  part  of  the  nineteenth 
century  penetrated  its  depths  and  reached  its  bottom. 

.  Soundings  are  now  made  with  much  accuracy,  even  to 
depths  of  four  miles  or  more.     Fine  steel  wire  is  used  for 


Fig.  35.    An  Ocean  Steamship 

a  line ;  the  sinker  is  a  heavy  iron  ball  that  is  automatically 
detached  on  touching  the  bottom ;  then  the  wire  is  rapidly 
reeled  in  by  steam  power.  A  sounding  of  3000  fathoms 
(one  fathom  equals  six  feet),  or  over  three  miles,  can  be 
completed  in  about  an  hour. 

The  temperature  of  the  deep  water  is  taken  by  self- 
registering  thermometers.  They  must  be  protected  by  an 
outer  glass  tube  against  the  tremendous  pressure  of  the 


THE  OCEAN 


99 


deep  water.  Samples  of  water  are  obtained  from  various 
depths  by  the  use  of  brass  tubes,  called  water  bottles,  sent 
down  open  but  automatically  closed  when 
reeling  in  begins.  Specimens  of  the  ocean 
bottom  are  gathered  by  dredges,  or  strong 
nets  with  an  iron  rim.  Wire  rope  is  needed 
to  haul  up  the  ton  or  more  of  material 
that  dredges  take  in  while  dragging  on 
the  sea  floor  at  depths  of  one,  two,  or  even 
three  miles.  Nets  are  sometimes  attached 
to  the  wire  rope  at  different  depths,  for 
the  purpose  of  catching  animals  that  hap- 
pen to  enter  them.  The  best  nets  are 
closed  while  sinking 
and  rising,  being  open 
only  while  trolling  at 
the  greatest  depth 
that  they  reach. 


Fig.  3(3 

Sounding  Instrument 

and  Water  Bottle 


71.  Ocean  Depths. — Soundings  have 
shown  that  the  ocean  basins  are  com- 
paratively steep  sided  and  flat  floored. 
The  greatest  depth  yet  found  is  31,614 
feet,  in  the  western  Pacific  near  the 
island  of  Guam  (lat.  12°  45'  N.,  long. 
145°  45'  E.).  Another  place  of  great 
depth,  30,930  feet,  is  in  the  Pacific, 
near  the  Fiji  islands. 

The  deepest  sounding  yet  made  in  the  Atlantic  is  27,366 
feet,  or  over  five  miles,  in  a  local  depression  100  miles  north 


mwm 


Fig.  37.    Dredge 


100  ELEMENTARY  PHYSICAL  GEOGRAPHY 

•of  Porto  Rico,  West  Indies.  The  Atlantic  is  generally  less 
deep  along  its  middle  (9000  to  12,000  feet)  than  on  either 
side  (15,000  to  18,000  feet),  the  shallower  middle  part 
being  sometimes  called  a  ridge  or  swell,     (See  Figm-e  144.) 

72.  Composition  and  Density.  —  The  ocean  contains  a 
great  variety  of  substances  in  solution,  for  it  has  received 
everything  that  streams  have  dissolved  and  carried  from 
the  lands  for  ages  past.  Common  salt  makes  three  quarters 
of  the  dissolved  substances.  An  important  but  much  less 
plentiful  dissolved  substance  is  limes^tone,  of  which  many 
sea  animals  make  their  shells  or  skeletons. 

A  small  quantity  of  atmospheric  gases  is  found  dis- 
solved in  sea  water,  even  in  its  deepest  parts.  The  gases 
are  taken  in  at  the  surface,  especially  when  air  is  caught 
in  dashing  waves.  It  is  upon  the  oxygen  thus  supplied 
that  fish  and  most  other  marine  animals  depend  for  breath- 
ing; but  whales  and  other  mammals  living  in  the  ocean 
come  to  the  surface  for  air. 

The  mineral  substances  dissolved  in  ocean  water  make 
about  three  per  cent  of  its  weight ;  their  presence  makes  it 
a  little  heavier  than  pure  water  (in  proportion  of  1.026  to 
1.000).  Although  water  is  easily  moved,  it  can  be  very 
little  compressed.  Hence,  in  spite  of  the  great  pressure  of 
the  upper  layers  of  the  ocean  on  those  beneath,  the  ocean 
is  unlike  the  atmosphere  in  being  of  nearly  uniform  density 
from  top  to  bottom.  Anything  that  is  heavy  enough  to 
sink  at  the  top  will  sink  all  the  way  to  the  bottom. 

73.  Color  and  Phosphorescence.  —  In  the  open  ocean,  far 
from  land,  the  water  is  extraordinarily  clear.     It  is  of  a 


THE  OCEAN  101 

beautiful  deep  blue,  so  strong  that  one  would  expect  the 
'  color  to  show  in  a  bucket ;  but  if  some  water  is  dipped  up 
from  the  sea  surface,  it  appears  perfectly  transparent  and 
colorless.  In  cloudy  weather  the  ocean  is  of  a  duller, 
more  leaden  hue.  Near  the  lands  the  blue  is  lighter  and 
turns  towaixi  a  greenish  shade.  Opposite  large  rivers  the 
water  may  be  yellowish  from  suspended  sediment;  the 
Yellow  sea  is  so  named  on  this  account.  What  large 
rivers  enter  it? 

There  are  many  small  jellylike  animals  that  float  in  the 
ocean.  Some  of  these  have  the  power  of  emitting,  when 
disturbed,  a  pale  light,  visible  in  the  dark.  They  are 
found  chiefly  in  the  warmer  parts  of  the  ocean.  Break- 
ing waves  and  the  foam  in  the  wake  of  a  vessel  may  thus 
become  beautifully  luminous  or  phosphorescent  at  night. 

74.  Ocean  Temperatures.  —  The  surface  layers  of  the 
ocean  vary  in  temperature  with  latitude,  reaching  about 
80°  around  the  equator,  and  being  reduced  to  30°  or  28° 
in  the  polar  regions  (Figure  44).  The  great  body  of  the 
deep  ocean  is  cold  in  all  latitudes ;  its  temperature  is  about 
30°  in  high  latitudes  and  35°  or  40°  in  the  torrid  zone. 

When  exploring  vessels  dredge  in  a  torrid  ocean  the 
sediments  brought  up  from  the  bottom  have  a  tempera- 
ture near  freezing,  strangely  in  contrast  with  that  of  the 
objects  on  shipboard  under  a  hot  sun. 

The  sun's  rays  have  small  effect  on  ocean  water  at 
depths  below  100  or  150  fathoms.  At  greater  depths  the 
ocean  must  be  nearly  dark,  with  hardly  perceptible  dif- 
ference between  day  and  night,  or  between  winter  and 


102  ELEMENTARY  PHYSICAL  GEOGRAPHY 

summer.  The  temperature  at  any  point  in  the  great  body 
of  the  deep  ocean  is  therefore  nearly  constant. 

Changes  of  temperature  in  the  ocean  surface  through 
the  day  or  the  year  are  very  small,  seldom  more  than  3° 
and  15°,  respectively. '  As  the  temperature  of  the  lower 
air  is  largely  controlled  by  that  of  the  surface  on  which 
it  rests,  the  climate  of  islands  in  mid  ocean  and  of  conti- 
nental borders- where  the  prevailing  winds  blow  ashore  is 
free  from  great  changes  of  temperature  between  winter 
and  summer. 

Salt  water  becomes  heavier  and  heavier  as  it  is  cooled 
down  to  its  freezing  point,  28°.  Hence  the  cold  surface 
water  of  high  latitudes  sinks  to  great  depths  and  creeps 
very  slowly  toward  the  equator;  thus  the  low  tempera- 
ture of  the  great  body  of  the  ocean  is  accounted  for. 

Fresh  water  is  unlike  salt  water  in  being  densest  at  39°. 
On  being  warmed  or  cooled  from  this  temperature  it  expands 
and  becomes  lighter.  Hence  in  winter,  when  all  the  water 
of  a  lake  has  been  cooled  to  39°,  further  cooling  affects  only 
the  surface  water,  which  may  then  soon  freeze. 

75.  Ice  in  the  Ocean.  —  Ice  expands  a  little  as  it  freezes ; 
it  therefore  floats,  about  one  seventh  of  its  volume  being 
out  of  water.  The  ice  formed  in  the  polar  oceans  is 
known  as  floe  ice ;  it  may  reach  a  thickness  of  from  three 
to  seven  feet  in  a  single  winter. 

Great  fields  of  floe  ice  drift  with  the  winds  and  currents. 
They  may  thus  be  torn  apart  or  crushed  together.  When 
two  floes  collide  pack  ice  of  very  irregular  surface  is 
formed;  it  may  reach  a  thickness  of  over  100  feet. 


THE  OCEAN 


103 


In  Greely's  expedition  to  the  Arctic  regions  in  1883 
his  boats  were  frequently  in  danger  of  being  crushed 
when  ice  fields  drifted  together,  closing  the  water  passage 
he  had  been  following. 

Smooth  floe  ice  is  easily  crossed  on  sleds.  The  Eskimos 
make  winter  journeys  upon  it.     Where  packed  it  may  be 


Pia.  38.    A  Vessel  beset  by  Pack  Ice 

impassable.  It  was  on  account  of  the  roughness  of  ridged 
pack  ice  that  Nansen  had  to  turn  back  from  his  "  dash  for 
the  pole,"  in  latitude  86°  13'  N.,  longitude  96°  E.,  on 
April  8,  1895.  When  two  large  fields  of  pack  ice  drift 
together  a  vessel  between  them  would  be  crushed,  unless 
of  great  strength  and  shaped  so  as  to  escape  by  rising. 
Nansen's  vessel,  the  "  Fram,"  was  especially  constructed 
to  withstand  great  pressure  and  so  survived  the  dangers 
to  which  it  was  exposed. 


104 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Icebergs  in  the  North  Atlantic  are  fragments  from  the 
ends  of  great  fields  of  ice  (glaciers)  that  descend  into  the 
sea  from  Arctic  lands,  chiefly  Greenland;  they  are  of 
fresh  water.  The  tabular  icebergs  of  the  Antarctic  ocean 
are  fragments  of  a  heavy  sheet  of  ice  around  the  south 
pole.     Some  of  these  ice  blocks  measure  a  mile  or  more 


Fig.  39.    An  Iceberg 

on  a  side,  and  1200  to  1500  feet  in  thickness.  Icebergs, 
being  of  fresh  water,  float  with  about  one  sixth  or  one 
seventh  of  their  volume  above  the  sea  surface. 

Collision  with  an  iceberg  is  one  of  the  dreaded  dangers 
of  navigation  in  high  latitudes.  In  the  southern  oceans 
drifting  icebergs  reach  latitude  50°,  or  even  40°.  In  the 
North  Atlantic  they  reach  latitude  45°,  southeast  of  New- 
foundland, but  they  are  absent  from  the  northwestern 
coast  of  Europe,  even  in  latitude  70°,  on  account  of  the 


THE  OCEAN 


105 


warm  water  there  prevailing.     They  are  wanting  in  the 
North  Pacific,  except  in  the  seas  of  northeastern  Asia. 

76.  The  Ocean  Bottom.  —  The  greater  part  of  the  deep 
ocean  bottom  is  a  comparatively  even  plain  of  soft  ooze. 
The  plain  rises  and  falls  gently  in  broad  swells,  but  is  not 


Fig.  40.    Globigeriua  (magnified  100  times) 

varied  by  hills  and  valleys  such  as  occur  on  the  lands. 
A  large  part  of  the  deep  sea  bottom  is  covered  with  a  fine 
deposit,  called  ooze,  which  consists  of  the  minute  shells, 
more  or  less  decayed,  of  simple  animal  forms  that  live  at 
or  near  the  surface.  One  of  these,  highly  magnified,  is 
shown  in  Figure  40.  In  the  deepest  oceans  the  bottom 
is  covered  with  a  fine  reddish  clay.     Nearer  the  shores 


106  ELEMENTARY  PHYSICAL  GEOGRAPHY 

the  deposits  become  muddy  with,  sediments  derived  from 
the  land.  It  is  by  the  very  slow  but  long-continued  accu- 
mulation of  these  deposits  that  the  ocean  floor  has  been 
made  so  smooth. 

"  The  monotony,  dreariness,  and  desolation  of  the  deeper 
parts  of  this  submarine  scenery  can  scarcely  be  realized. 
The  most  barren  terrestrial  districts  must  seem  diversified 
when  compared  with  the  vast  expanse  of  ooze  which  covers 
the  deeper  parts  of  the  ocean." 

No  mountain  ranges  with  sharp  peaks  and  ridges 
separated  by  deep  passes  and  valleys  have  yet  been  dis- 
covered on  the  open  ocean  floor  far  from  the  conti- 
nents; but  Cuba  and  some  of  the  neighboring  islands 
in  the  "West  Indies  seem  to  be  the  crests  of  a  mountain 
range  whose  western  extension  forms  submarine  ridges 
in  the  northern  Caribbean,  connecting  the  islands  with 
Central  America. 

Volcanic  and  coral  islands  rise  with  steep  slopes  from 
the  deep  ocean.  Volcanic  cones  sometimes  rise  above  the 
ocean  surface,  forming  lofty  mountains,  as  in  the  Hawaiian 
islands;  sometimes  they  are  known  only  by  soundings, 
their  summits  being  below  sea  level. 

77.  Mediterraneans. — Besides  the  open  oceans  thus  far 
considered  there  are  several  deep  seas,  more  or  less  separated 
from  the  oceans  by  land  barriers.  The  most  important  of 
these  is  the  classic  Mediterranean  (the  sea  "  in  the  middle 
of  the  lands  ") ;  its  average  depth  is  nearly  as  great  as  that 
of  the  great  oceans,  but  it  is  connected  with  the  Atlantic 
only  by  the  narrow  and  shallow  Strait  of  Gibraltar. 


THE  OCEAN  107 

Other  similar  mediterranean  seas  are  the  Caribbean  and 
the  Mexican  (deep  central  part  of  the  Gulf  of  Mexico), 
adjoining  the  western  Atlantic ;  and  the  Japan,  China, 
Sulu,  and  some  smaller  seas  imperfectly  inclosed  from 
the  western  Pacific  by  island  chains.  The  deep  water 
of  mediterraneans  is  warmer  than  that  of  the  neighbor- 
ing oceans,  whose  cold  bottom  waters  cannot  enter  the 
inclosed  basins. 

78.  Continental  Shelves.  —  The  ocean  often  overlaps 
the  borders  of  the  continental  masses  in  a  comparatively 
shallow  belt  of  water,  at  whose  outer  edge  the  depth  is 
commonly  about  600  feet;  thence  it  rapidly  sinks  to  the 
deep  ocean  floor.  These  shallow  bottoms  are  known  as 
continental  shelves.  The  water  on  the  shelf  is  often 
greenish  from  fine  suspended  sediment,  unlike  the  clear 
deep  blue  water  of  the  open  ocean. 

A  well-defined  continental  shelf,  from  50  to  100  or 
more  miles  in  width,  stretches  along  the  eastern  side  of 
North  America  from  Newfoundland  to  Florida,  and  thence 
around  the  Gulf  of  Mexico.  The  British  Isles  stand  upon 
a  continental  shelf  that  borders  mid-westem  Europe.  The 
Malayan  and  Australasian  islands  surmount  broad  shelves 
between  Asia  and  Australia,  separated  by  a  belt  of  deeper 
water. 

The  gravel,  sand,  and  clay  washed  from  the  lands  into 
the  seas  are  moved  about  by  waves,  currents,  and  tides 
on  the  continental  shelves.  Thus  the  land  waste  is  slowly 
ground  finer  and  finer,  and  its  finest  particles  are  gradu- 
ally moved  outward  to  deeper  water.     They  are  seldom 


108 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


found  in  dredgings  over  200  miles  from  shore;  for  the 
most  part  they  are  carried  a  less  distance. 

In  the  course  of  years,  centuries,  and  ages  the  sedi- 
ments thus  accumulating  on  a  continental  shelf  may 
form  successive  layers,  each  a  few  inches  or  feet  in 
thickness,  according  to  the  rate  of  supply.  A  layer  of 
sediments  of  this  kind  is  called  a  bed  or  stratum  (plural, 
strata).     Many  strata  laid  down   on   the   sea   floor,  one 


Continent 


Cf  Shallow  Water  on 

Cq      Con fi ami al  Shelf 


Deep  Water 


Fia.  41.     Section  of  Continental  Shelf 

after  another,  may  form  a  heavy  deposit  hundreds  of 
feet  in  thickness,  including  many  shells  and  other  relics 
of  marine  life. 

As  new  strata  are  added,  the  older  strata  are  buried 
deeper  and  deeper,  their  grains  are  more  or  less  cemented 
together  by  'mineral  substances  deposited  upon  them  by 
slowly  infiltrating  waters,  and  thus  they  gain  a  firm 
texture.  It  is  chiefly  in  this  way  that  layers  of  loose 
sediments  are  changed  into  layers  of  solid  rock. 

The  lowland  borders  of  continents  are  often  built  of 
layers  of  sand  and  clay  frequently  containing  marine 
fossils;  this  suggests  that  a  former  continental  shelf  has 
there  been  raised  to  a  land  surface. 

The  shallower  waters  of  continental  shelves  are  of 
great   importance    as   the    chief   fishing   grounds    of   the 


THE  OCEAN 


109 


world.  The  European  ports  around  the  North  sea  send  out 
hundreds  of  fisliing  vessels  to  its  shallow  waters.  The 
rich  fishing  grounds  of  the  Newfoundland  banks  attracted 
many  fishermen  from  the  Old  World  over  thi-ee  centuries 
ago.  They  ai'e  still  resorted  to  every  year  by  fishermen 
from  New  England,  chiefly  from  Gloucester,  JVIassachusetts. 
Although  far  out  of  sight  of  land,  the  water  on  the  banks 


Fig.  42.    Orbital  Movement  of  Water  in  Waves 


is  so  shallow  that  fishing  schooners  (such  as  the  one  shown 
in  Figure  42)  may  ride  at  anchor  while  their  men  go  off  in 
small  boats  to  fish  with  nets  or  with  hook  and  line.  Dur- 
ing fogs,  which  are  frequent,  there  is  danger  of  collision 
with  transatlantic  steamers,  whose  route  leads  them  through 
the  fishing  grounds. 

79.  Waves.  — Wind  blowing  over  the  sea  forms  waves  that 
follow  the  wind.  The  water  in  the  waves  moves  only  up  and 
down,  back  and  forth,  with  very  small  forward  motion.    The 


110'  ELEMENTAKY  PHYSICAL  GEOGRAPHY 

stronger  the  wind,  the  higher  the  crests  and  the  deeper  the 
troughs  of  the  waves,  the  greater  their  length  (distance  from 
crest  to  crest),  and  the  faster  their  forward  motion. 

The  arrows  in  the  front  section  of  Figure  42  show  the 
movement  of  the  water  at  the  moment  when  the  waves  have 
the  form  there  drawn.  The  ovals  show  the  path  of  the  water 
as  the  waves  roll  by.  The  independence  of  wave  and  water 
movement  may  be  seen  on  a  river  surface  when  the  wind  is 
blowing  upstream  ;  or  at  the  mouth  of  a  harbor  when  the 
wind  is  blowing  on  shore,  while  the  tide  is  running  out. 

Great  waves  formed  in  the  open  ocean  by  gales  and  hur- 
ricanes are  often  called  seas.  Their  height  from  trough  to 
crest  reaches  30  or  40  feet,  but  seldom  exceeds  50  feet. 
Their  length  varies  from  300  to  1500  feet  or  more,  and 
their  velocity  from  20  to  60  miles  an  hour.  The  interval 
between  the  passage  of  successive  crests,  or  the  period 
of  the  wave,  is  seldom  more  than  10  or  12  seconds. 

80.  The  Use  of  Oil  in  Storms.  —  A  small  quantity  of 
oil  poured  on  the  sea  spreads  rapidly  and  reduces  the 
violence  of  the  waves  in  a  storm.  A  gale  ordinarily 
forms  ripples  and  small  waves  on  the  backs  of  greater 
waves  and  causes  the  crests  of  great  seas  to  curl  over, 
so  that  they  would  break  with  destructive  force  on  the 
deck  of  a  vessel.  At  such  a  time  a  film  of  oil  decreases 
the  catch  of  the  wind  on  the  water  and  prevents  the  large 
waves  from  curling  and  breaking. 

Many  accounts  of  the  use'  of  oil  in  storms  have  been 
published  by  the  United  States  Hydrographic  Office, 
Washington.     They  show  that  when  a  vessel  is  headed 


THE  OCEAN  111 

toward  the  wind  ("  hove  to ")  and  heavy  seas  come  on 
board  over  the  bow,  a  little  oil  allowed  to  drip  from  a 
bag  will  spread  even  toward  the  wind,  forming  a  smooth 
surface,  or  "  slick,"  and  the  waves  entering  the  slick  will 
decrease  in  height  and  cease  breaking  over  the  deck. 

When  a  vessel  is  running  with  the  wind  heavy  seas 
sometimes  come  aboard  over  the  stern;  but  if  a  little  oil 
is  allowed  to  diip  overboard,  the  slick  spreads  out  like  a 
fan  across  the  wake,  and  the  great  seas  are  rounded  off 
as  they  run  into  it,  so  that  the  vessel  rides  them  without 
difficulty. 

81.  Swell  and  Surf.  —  Great  waves,  traveling  twenty 
to  sixty  miles  an  hour,  soon  run  out  of  the  storm  that 
forms  them  and  swing  far  across  the  ocean,  preserving 
their  length  and  velocity,  but  diminishing  in  height.  In 
this  reduced  form  a  wave  is  called  a  swell. 

In  calm  weather  the  ocean  surface  may  be  smooth  and 
glassy,  but  not  absolutely  level  and  quiet ;  for  it  is  never 
free  from  the  slow  heaving  and  sinking  of  fading  swells 
from  distant  storms.  A  vessel  becalmed  in  the  doldrums 
always  swings  idly  to  and  fro  as  the  swell  rolls  by. 

When  the  swell  runs  into  shoaling  water  close  to  land 
its  velocity  decreases,  its  crest  rises  and  its  trough  sinks, 
thus  making  its  height  greater ;  the  front  becomes  steeper 
than  the  back.  The  swell  thus  becomes  higher  and  higher 
as  it  advances.  If  it  arrives  on  a  long,  smooth,  gently  slop- 
ing beach,  the  water  before  the  advancing  wave  becomes  so 
shallow  that  it  cannot  build  up  the  wave  front ;  then  the 
crest  curls  evenly  forward  in  long  lines  nearly  parallel 


112 


ELEMENTARY  PHYSICAL  'GEOGRAPHY 


with  »the  shore  and  dashes  with  a  roaring  noise  upon  the 
beach,  in  the  form  of  surf  or  breakers. 

The  surf  is  like  a  mill  in  which  cobbles,  gravel,  and  sand 
on  a  beach  are  ground  finer  and  finer.  The  pebbles  can 
be  heard  rattling  as  they  are  rolled  back  and  forth. 


Fig.  43.     Surf 


Exposed  beaches  may  be  beaten  by  a  heavy  surf,  ten  or 
fifteen  feet  high,  while  the  neighboring  sea  is  unruffled  by 
the  wind.  The  surf  is  then  derived  from  a  broad  swell 
which  comes  from  the  great  waves  of  a  storm  that  may  be 
a  thousand  or  more  miles  away. 

The  great  hurricane  of  Sept.  3-12,  1889^  while  on  its 
way  from  the  West  Indies  to  the  Carolina  coast,  produced  a 
destructive  surf  on  the  long  beaches  of  New  Jersey  while  the 
storm  area  was  still  a  thousand  miles  distant.    At  St.  Helena, 


THE  OCEAN  113 

a  lonesome  island  in  the  South  Atlantic,  boats  from  vessels 
at  anchor  in  the  harbor  frequently  cannot  reach  the  shore 
in  fair  weather  on  account  of  the  "  rollers,"  or  heavy  surf, 
on  the  beach.  The  swell  that  produces  this  surf  is  believed 
to  come  from  storms  far  away  in  temperate  latitudes  of  the 
North  Atlantic. 

When  waves  riui  upon  a  steep  and  rocky  shore  they 
dash  unevenly  against  the  ledges,  foaming  and  fretting 
as  they  sweep  back  and  forth.  Dui'ing  storms  spray 
may  be  flung  up  50  or  100  feet  into  the  air.  These  great 
waves  exert  an  enormous  force,  capable  of  moving  blocks 
of  rock  ten  or  more  feet  in  diameter.  Wave  work  is  not 
then  limited  to  the  immediate  shore  line;  loose  materials 
in  depths  of  ten,  twenty,  or  more  fathoms  are  moved  about 
and  ground  smaller  and  smaller,  and  the  finest  grindings 
are  swept  away  to  deeper,  quieter  water. 

82.  Earthquake  Waves.  —  When  an  earthquake,  caused 
by  some  disturbance  in  the  earth's  crust,  occurs  beneath 
the  sea  the  whole  body  of  the  ocean  above  it  is  moved 
slightly,  and  the  movement  then  spreads  away  on  all  sides 
in  long,  low  waves  that  travel  with  great  speed.  When 
nearing  the  shore  the  speed  and  length  of  the  wave  are 
decreased,  but  the  height  is  greatly  increased.  The  wave 
may  then  rush  fax  in  on  a  lowland  coast,  causing  great 
destruction. 

The  tremendous  explosive  eruption  of  the  volcanic 
island  Krakatoa,  between  Java  and  Sumatra,  in  August, 
1883,  produced  waves  that  spread  far  around  the  world. 
Their  average  velocity  of  progression  was  nearly  400  miles 


114  ELEMENTARY  PHYSICAL  GEOGRAPHY 

an  hour.  On  distant  coasts  their  rise  and  fall  was  slight, 
but  on  coasts  near  Krakatoa  the  waves  rushed  upon  the 
land  with  a  height  of  from  fifty  to  eighty  feet,  flooding  the 
lowlands,  sweeping  away  many  villages,  and  drowning 
thousands  of  the  inhabitants.  A  large  vessel  was  carried 
a  mile  and  a  half  inland  and  stranded  thirty  feet  above  sea 
level. 

An  earthquake  in  the  North  Pacific  produced  a  destruc- 
tive wave,  from  ten  to  fifty  or  more  feet  high,  on  the  coast 
of  northern  Japan  in  the  evening  of  June  15,  1896.  The 
coast  was  laid  waste  for  175  miles.  The  few  persons  who 
saw  the  wave  and  survived  it  reported  that  the  sea  first 
drew  back  about  a  quarter  of  a  mile  and  then  came  rushing 
in  like  a  black  wall,  gleaming  with  phosphorescent  light 
and  overwhelming  the  shore.  On  the  open  coast  the  sea 
became  quiet  in  a  few  minutes  after  the  wave  broke,  but 
in  bays  the  waters  surged  and  swirled  for  half  an  hour. 
The  outline  of  the  shore  was  changed  in  many  places; 
many  villages  were  destroyed,  and  thousands  of  acres  of 
arable  land  were  laid  waste.  Thousands  of  fishing  boats 
were  crushed  or  carried  away;  27,000  persons  lost  their 
lives,  and  60,000  survivors  were  left  homeless. 

83.  Ocean  Currents.  —  The  upper  waters  of  the  ocean, 
to  a  depth  of  50  or  100  fathoms,  move  slowly  in  the  gen- 
eral direction  of  the  prevalent  winds,  thus  forming  currents 
that  circulate  about  the  great  oceanic  areas.  The  general 
course  of  the  ocean  currents  is  such  that  each  of  the  large 
oceans  possesses  a  great  eddylike  current  that  moves 
slowly  around  it,  leaving  the  central  waters  almost  quiet. 


THE  OCEAN  115 

Exercise.  How  many  systems  of  eddying  currents  are  shown  in 
Figure  44  ?  Which  one  is  the  largest  ?  Which  three  smaller  ones 
are  of  about  the  same  size  ?  In  what  ways  are  the  eddying  currents 
alike  ?  In  what  different  ?  Compare  their  movements  along  the  west 
coasts  in  middle  latitudes;  along  east  coasts.  How  do  they  move 
near  the  equator?  Note  the  long  equatorial  countercurrent  in  the 
Pacific,  separating  the  two  great  eddies,  north  and  south.  Note  the 
-connecting  current  between  the  two  eddies  of  the  Atlantic.  Compare 
the  general  courses  of  the  winds,  Figures  22  and  23,  with  the  courses 
of  the  ocean  currents.  Name  some  districts  where  the  winds  and 
currents  agree. 

The  remarkable  cor.  3spondence  between  the  course  of 
the  oceanic  eddies,  Figure  44,  and  the  course  of  the  pre- 
vailing winds  over  the  oceans,  as  shown  in  the  charts, 
Figures  22  and  23,  points  to  the  winds  as  the  cause  of  the 
currents.  Like  the  circulation  of  the  atmosphere,  the  eddy- 
ing of  the  upper  waters  of  the  oceans  must  be  regarded  as 
a  characteristic  of  a  globe  having  large  oceans,  a  mobile 
atmosphere,  and  a  warm  equatorial  zone. 

The  belief  that  the  winds  cause  the  currents  is  confirmed 
by  the  way  in  which  the  surface  drift  of  the  waters  may  be 
for  a  time  brushed  to  one  side  of  its  usual  course,  or  even 
reversed,  during  a  storm. 

If  an  observer  stood  in  the  center  of  an  oceanic  eddy  in 
the  northern  hemisphere,  the  currents  would  pass  around 
him  from  left  to  right,  or  clockwise;  in  the  southern 
hemisphere,  from  right  to  left,  or  counter-clockwise. 

The  eddying  currents  are  the  chief  natural  basis  for  sub- 
dividing the  great  oceanic  area  into  the  six  oceans;  the 
North  and  South  Pacific,  the  North  and  South  Atlantic, 
and  the  Indian  oceans  each  having  its  own  great  eddy, 


116 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


while  the  Antarctic  ocean  has  a  great  eddy  around  the 
south  pole,  joining  the  eddies  of  the  three  southern  oceans. 
The  Arctic  also  has  a  current  about  the  pole  joining  that 
of  the  North  Atlantic,  somewhat  like  the  two  loops  of  a 
figure  8 ;  but  the  Arctic  should  be  classified  as  a  large  sea 
or  gulf  rather  than  as  an  ocean. 

A  broad  and  shallow  current  that  advances  at  a  rate  of 
ten  or  fifteen  miles  a  day,  like  that  which  crosses  the 

middle  North  Atlantic, 
should  be  called  a  drift, 
A  narrow  current,  flow- 
ing with  a  velocity  of 
fifty  or  more  miles  a  day, 
like  that  issuing  from 
the  Gulf  of  Mexico 
through  the  Strait  of 
Florida,  should  be  called 
a  stream. 
It  is  important  that  the  masters  of  vessels  should  be 
acquainted  with  the  movements  of  ocean  currents.  In 
cloudy  and  foggy  weather,  when  observations  of  the  sun 
cannot  be  made  to  determine  latitude  and  longitude, 
a  vessel  might  be  drifted  out  of  its  expected  course 
if  no  allowance  were  made  for  the  movement  of  the 
waters.  Thus,  if  a  vessel  intending  to  follow  the  course 
MdbcN^  Figure  45,  were  drifted  to  the  course  MABCE, 
it  would  pass  dangerously  near  the  headlands  at  JB  and  C, 
and  might  even  run  ashore.  Wrecks  on  the  south- 
west coast  of  Ireland  have  not  infrequently  been  due 
to  this  cause. 


Fig.  45. 


Displacement  of  a  Vessel  by- 
Currents 


THE  OCEAN 


117 


In  Nansen's  famous  attempt  to  reach  the  north  pole  he 
sailed  eastward  along  the  northern  coast  of  Asia  and 
turned  northward  into  a  region  of  ice  fields,  where  his 
vessel  was  caught  between  two  floes.  He  then  drifted 
with  the  ice,  expecting  that  the  Arctic  current  would 
carry  him  past  the  pole  toward  Greenland.  Had  he  gone 
further  east  before 
turning  north,  a  closer 
approach  to  the  pole 
might  have  been  made. 

The  drift  of   aban- 
doned   wrecks,   whoso 
positions  are  noted  by 
passing  vessels,  gives 
indications    of    the 
movements    of    cur- 
rents.     The     angular 
lines    in     Figure     46 
show  the  drift  of  sev- 
eral wrecks.     The  broken  lines  indicate  the  drift  of  many 
logs  from  a  great  timber  raft  that  was  abandoned  in  a 
storm 'while  on  the  way  from  the  Canadian  provinces  to 
New  York,  December,  1887. 

Thousands  of  bottles  have  been  thrown  into  the  sea,  with 
record  of  the  time  and  place  where  they  have  been  set  adrift 
and  request  that  the  finder  shall  report  the  time  and  place 
of  their  discovery,  afloat  or  ashore.  The  dotted  lines  of 
Figure  46  give  a  few  inferred  "bottle  tracks." 

The  several  parts  of  the  various  eddies  may  receive  spe- 
cial names.     Those  parts  which  run  westward,  near  and 


Fia.  46. 


Drift  of  Floating  Objects  by 
Currents 


118  ELEMENTARY  PHYSICAL  GEOGRAPHY 

about  parallel  to  the  equator,  are  called  the  equatorial  cur- 
rents. The  eastern  part  of  the  South  Pacific  eddy  is  called 
the  Humboldt,  or  Peruvian,  current ;  it  brings  a  great  body 
of  cool  water  from  far  southern  latitudes. 

The  name  Gulf  Stream,  in  the  Atlantic,  should  be  lim- 
ited to  the  narrow,  deep,  and  rapid  current  which  issues 
from  the  Gulf  of  Mexico  with  a  velocity  of  eighty  miles 
a  day;  the  name  is  popularly,  but  incorrectly,  extended 
far  northeast  over  the  broad,  shallow,  and  slow-moving 
drift  on  the  northern  side  of  the  North  Atlantic  eddy,  and 
even  along  its  branch,  past  Norway.  This  extension  of  the 
current  is  not  a  stream  at  all,  and  it  includes  much  water 
that  passed  outside  of  the  West  Indies  and  not  through 
the  Gulf  of  Mexico. 

Sailing  vessels  should  take  advantage  of  winds  and  cur- 
rents in  shaping  their  courses.  If  bound  from  the  eastern 
United  States  to  far  South  American  ports,  they  should 
cross  the  equator  well  to  the  eastward,  so  as  to  avoid  being 
carried  backward  by  a  strong  current  past  the  Guiana  coast, 
where  the  winds  may  fail  in  the  doldrums.  A  ship  sailing 
from  an  Atlantic  port  to  Australia  should  round  Cape  of 
Good  Hope  and  take  advantage  of  favorable  winds  and 
currents  in  the  southern  Indian  ocean  about  latitude  50°. 
On  the  homeward  voyage  favoring  winds  and  currents 
would  be  found  in  the  same  latitude  of  the  South  Pacific, 
toward  Cape  Horn. 

84.  Currents  and  Temperatures.  —  Currents  influence 
the  distribution  of  temperature  in  the  oceans  and  in  the 
winds  that  blow  over  them.     In  the  North  Atlantic,  for 


THE  OCEAN  119 

example,  a  broad  drift  of  rather  warm  water  flows  north- 
east in  middle  latitudes,  past  the  British  Isles  and  Nor- 
way ;  while  a  cold  current  returning  from  the  Arctic  regions 
flows  southward  past  Labrador  and  Newfoundland.  Hence, 
in  the  same  latitude,  winds  from  the  sea  are  mild  in  north- 
western Europe  and  cliilling  in  northeastern  America. 

In  winter  the  harbors  of  the  Labrador  and  Greenland 
coast  are  closed  with  ice ;  harbors  in  the  same  latitude  on 
the  eastern  side  of  the  Atlantic  remain  open  all  the  year 
round.  In  what  countries  are  these  harbors  situated? 
Northern  Norway  has  a  milder  climate  than  any  other 
country  at  so  great  a  distance  from  the  equator.  Why 
is  this?  What  land  in  the  southern  hemisphere  is  as 
far  from  the  equator  as  Norway? 

The  southern  coast  of  Alaska  has  a  comparatively  mild 
climate  on  account  of  the  northeastward  drift  of  the  sur- 
face waters  in  the  North  Pacific  eddy.  The  cool  Peruvian 
current  keeps  the  temperature  so  low  about  the  Galapagos 
islands  (near  the  equator  west  of  Peru)  that  coral  reefs, 
such  as  abound  further  west  in  the  equatorial  Pacific, 
are  not  found  on  their  shore. 

85.  Tides.  —  Regular  movements  of  the  ocean,  rising 
and  falling  on  the  shores  twice  in  a  little  more  than  a  day 
(twenty-four  hours,  fifty-two  minutes),  are  called  tides.  In 
the  open  ocean  tides  are  not  perceived ;  but  in  many  bays 
the  tidal  change  of  level,  or  range,  reaches  ten,  twenty,  or 
more  feet.  The  highest  stage  of  the  tide  is  called  high  tide 
or  high  water;  the  lowest  stage,  low  tide  or  low  water. 
The  change  of  level  is  accompanied  by  currents, — flood  tide 


120 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


running  in  from  the  ocean,  ebb  tide  running  out  again.  A 
brief  period  of  quiet,  or  "  slack  water,"  occurs  when  flood 
changes  to  ebb,  or  ebb  to  flood.  The  vessels  that  are  aground 
at  low  tide  in  Figure  47  would  be  afloat  at  high  tide. 


Fig.  47.    Low  Tide  in  a  Harbor 

The  tidal  undulations  of  the  oceans  are  caused  chiefly  by 
the  attraction  of  the  moon ;  they  are  somewhat  affected  by 
the  attraction  of  the  sun. 

Tidal  currents  are  beneficial  in  maintaining  a  circulation 
in  bays  and  harbors  where  the  waters  might  otherwise  be 
almost  stagnant.  At  high  water  a  harbor  will  admit  ves- 
sels of  a  larger  size  than  c©uld  enter  if  the  ocean  level 
did  not  change ;  but  at  low  water  the  harbor  may  be  inac- 
cessible except  to  much  smaller  vessels.  The  hour  of 
departure  of  ocean  steamers  is  usually  determined  by  the 


&M 

\ 

■^■^'  _ 

__^z-^r_j^-:__       ..^^*-W^ 

.imMBI 

li 

THE  OCEAN 


121 


hour  of  high  tide,  so  that  they  may  have  water  as  deep  as 
possible  when  leaving  their  harbor. 

In  funnel-shaped  bays  or  estuaries  the  tidal  range 
becomes  large,  and  flood  and  ebb  currents  are  very  strong, 
makmg  navigation  difficult  or  even  dangerous.  The  tidal 
range  sometimes  exceeds  fifty  feet  m  the  estuaries 'at  the 
head  of  the  Bristol  channel  in  western  England,  and  of 
the  Bay  of  Fundy  in  New  Brunswick ;  in  the  latter  the  flood 


Fig.  48.    The  Tidal  Wave,  or  Bore,  in  the  Seine 

current  rushes  in  like  foaming  surf,  shown  in  Plate  V. 
The  estuary  of  the  Seine  in  northwestern  France  has  a 
similar  surf-like  tide,  shown  in  Figure  48.  Such  surf-like 
tides  are  called  bores.  A  bore  occurs  at  the  mouth  of  the 
Amazon;  it  is  so  violent  on  the  northern  side  of  the  river 
near  the  sea  that  the  shore  line  is  rapidly  worn  back,  and 
hence  no  important  settlements  have  been  made  there. 

Where  tidal  currents  are  thus  strengthened  they  sweep 
the  sediments  of  the  shallow  bottom  back  and  forth, 
grinding  them  finer  and  finer.     The  finest  particles  thus 


122 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


produced  are  slowly  drifted  offshore,  where  they  settle  in 
deep  water.  When  a  gale  is  blowing  and  producing 
waves  in  strong  flood  or  ebb  currents  their  work  on  the  bot- 
tom is  much  increased ;  for  the  sediments  are  slightly  raised 
from  the  bottom  by  the  agitation  of  the  waves,  and  thus 
they  are  brought  more  into  the  power  of  the  tidal  currents. 

Many  curious  tidal  phe- 
nomena are  found  on  shore 
lines  of  different  forms. 
At  New  York  a  high  tide 
entering  from  the  harbor 
reaches  the  rocky  narrows 
of  Hell  Gate  when  a  low 
tide  arrives  through  Long 
Island  sound ;  and  six 
hours  later  a  low  tide 
from  the  harbor  meets  a 
high  tide  from  the  sound. 
Thus  a  rapid  current  is 
caused  to  flow  back  and 
forth  in  the  narrow  pas- 
sage, which  was  danger- 
ous to  vessels  until  the  channel  was  widened  by  blasting 
away  its  reefs.  A  current  of  this  kind  is  sometimes  called 
a  tidal  race. 


Fig.  49.    Jellyfish  floating  in  Sea  Water 


86.  Life  in  the  Ocean.  —  The  surface  layers  of  the  open 
ocean  possess  a  considerable  variety  of  animal  life,  from 
large  mammals,  like  whales,  to  minute  organisms.  Figure 
40,  whose  tiny  shells  are  so  plentifully  strewn  over  the 


THE  OCEAN 


123 


Fig.  50.    Deep-Sea  Fish. 


ocean  floor.     The  former  occur  in  moderate  numbers ;  the 

latter  are  countless.     The  distribution  of  surface  life  is 

determined  chiefly  by  differences  of  temperature  from  the 

torrid  to  the 

frigid   zones. 

Those   forms 

which    swim 

or  are  drifted 

freely  by  the  currents  are  found  over  vast  areas.     In  fair 

weather  the  surface  waters  are  sometimes  alive  with  minute 

jellylike  forms. 

The  nearly  quiet  water  about  the  central  part  of  the 
great  eddying  currents  generally  contains  a  considerable 
quantity  of  floating  seaweed,  or  sar- 
gassum;  hence  these  central  areas  are 
called  sargasso  seas.  The  sargassum  is 
believed  to  be  derived  from  shore 
waters,  where  it  grows  on  the  shallow 
bottom.  A  great  variety  of  small  ani- 
mals live  on  the  floating  weed,  and  a 
certain  kind  of  fish  uses  the  weed  as 
a  "nest"  for  its  eggs. 

The    intermediate    depths    of    the 
ocean,  between  the  upper  part   and 
the  bottom,  are  prevailingly  without 
life,  — a  great  desert  space,  cold,  quiet, 
and  monotonous. 
The  deep  ocean  floors  have  no  plants.     They  are  inhab- 
ited by  a  considerable  variety  of  animals,  such  as  fish, 
crabs,  shellfish,  starfish,  etc.;  but  the  forms  of  life  are 


Fig.  51 
Deei>-Sea  Crustacean,  x  J 


124  ELEMENTARY  PHYSICAL  GEOGRAPHY 

here  much  less  varied  and  less  numerous  than  in  the 
shallower  waters  near  the  shore. 

While  many  deep-sea  animals  are  blind,  it  is  curious 
that  some  have  well-formed  eyes  and  are  ornamented  with 
colors.  Colors  would  be  useless  if  they  could  not  be  seen, 
and  eyes  would  be  of  no  service  in  complete  darkness. 
Hence  there  must  be  some  light  in  the  ocean  abysses.  As 
sunlight  cannot  penetrate  to  great  depths,  the  light  may 
be  supplied  by  phosphorescent  animals,  of  which  there 
are  many  kinds  in  the  deep  sea. 

The  shallow  waters  of  the  ocean  margin  teem  with  plants 
and  animals.  Many  animals,  such  as  sponges,  corals,  and 
barnacles,  are  fixed  to  the  bottom;  they  need  not  move 
about  in  search  of  food,  because  the  moving  waters  bring 
it  to  them.  Nearly  all  the  plants  of  the  sea  are  of  a  com- 
paratively simple  kind,  without  flowers  or  seeds.  The 
shallow  waters  are  the  fishing  grounds  of  the  sea  and  fur- 
nish important  supplies  of  food  to  the  neighboring  lands. 

Supplement  to  Chapter  III 

87.  The  Cause  of  the  Tides.  —  Note  the  time  when  the  moon 
passes  over  the  south  point  of  the  horizon  on  two  successive  days. 
(These  observations  may  be  made  in  the  early  evening  when  the 
moon  is  near  its  first  quarter.  If  daytime  observations  are  pre- 
ferred, they  may  be  made  in  the  early  forenoon  when  the  moon  is 
between  third  quarter  and  new ;  or  in  the  late  afternoon  between 
new  moon  and  first  quarter.)  How  long  is  the  interval  between  the 
two  passages  ?  Compare  this  interval  with  that  between  two  high 
tides,  as  stated  on  page  119.     How  are  the  two  intervals  related? 

The  above  comparison  shows  that  the  tides  in  some  way  depend 
on  the  moon,  because  two  sets  of  tides  occur  in  the  time  (24  hours 


THE  OCEAN 


125 


0 


Fig.  52 


52  minutes)  between  two  successive  passages  of  the  moon  across  the 
meridian.  It  can  be  shown  that  the  attraction  of  the  moon  on  the 
oceans  tends  to  cause  high  tides,  //' 
and  //",  Figure.  52,  on  opposite  sides 
of  the  earth  near  the  equator,  with  low 
tides,  0'  and  0",  between  them.  Thejf^ 
tides  tend  to  preserve  a  constant  posi- 
tion with  respect  to  the  moon,  some- 
what as  indicated  in  the  figure.     Hence  as  the  earth  turns  round 

(the  axis  standing  at  right  angles  to 
the  paper),  any  point  in  the  equa- 
torial oceans  must  pass  H',  0\  H", 
0"  in  24  hours  52  minutes,  and 
must  therefore  experience  two  high 
and  two  low  tides  in  that  period. 
The  moon  tends  to  form  similar 
but  weaker  tides  around  all  the  lati- 
tude circles  in  the  two  hemispheres. 
The  sun  also  tends  to  cause  tides ; 
but  in  spite  of  the  vastly  greater 
size  of  the  sun  than  of  the  moon, 
the  sun  is  so  much  farther  away 
that  the  solar  (sun)  tides  have  only 
®       ^k^y^  [  ^  about  one  third  of  the  strength  of 

^  -    -     -.  ^Yie  lunar  (moon)  tides. 

At  new  moon,  when  the  sun  and 
moon  are  on  the  same  side  of  the 
earth,  as  in  Figure  53,  the  lunar  (L) 
and  solar  (S)  tides  act  together,  and 
hence  the  rise  and  fall  of  the  tides, 
or  the  tidal  range,  is  increased.  At 
first  quarter  the  line  to  the  moon  is 
at  right  angles  to  that  to  the  sun, 
as  in  Figure  54.  Here  the  sun  tries  to  make  a  low  tide  where  the 
moon  makes  a  high  tide,  L ;  and  the  moon  makes  a  low  tide  where 


iG 

1st  Day 
/  New  Moon 

Spring  Tides 

Fio.  53 

hi 

7th  Day 
First  Quarter 

sV^ 

^'    Neap  Tides 

Fig.  54 

,  /^- 

14th.Day 
.^S'FuUMoon 

^G 

y 

S^^-^ 

Spring  Tides 

Fig.  55 

& 

,     21stDay              > 
Third  Quarter      / 

^^il 

\ 

Neap  Tides 

®- 


ria.66 


126 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


the  sun  tries  to  make  a  high  tide,  S.  As  a  result,  the  tidal  range 
is  weakened.  How  do  the  lunar  and  solar  tides  combine  at  time  of 
full  moon,  Figure  55  ?  at  time  of  third  quarter,  Figure  56  ? 

It  thus  appears  that  in  the  twenty-eight  days  between  two  new 
moons,  or  about  a  month,  the  tidal  range  is  strong,  weak,  strong,  and 
weak.  At  the  times  of  strong  range  the  tides  are  called  spring  tides ; 
at  times  of  weak  range,  neap  tides.  The  variation  of  tidal  range 
from  new  moon  to  fuU  moon  is  shown  in  Figure  57.  How  often 
does  the  period  of  spring  tides  occur  in  a  month  ?  of  neap  tides  ? 

It  is  not  possible  at  present  to  state  how  the  tides  behave  in  the 
open  ocean ;  they  cannot  be  observed  in  deep  water,  far  from  shore. 


Juuyuu 
'D 


^ "  li  U 11 U II U  I)  I 


Fig.  57.    Variation  of  Tides  for  Two  Weeks 


They  are  known  only  as  they  come  upon  the  shores  of  islands  and 
continents.  Their  strength  then  depends  not  only  on  the  combina- 
tion of  lunar  and  solar  forces,  as  in  spring  tides  and  neap  tides,  but 
still  more  on  the  form  of  the  shallowing  sea  floor  and  of  the  shore 
line.  Just  as  swell  is  increased  in  height  as  it  runs  ashore,  so  are 
the  tides;  for  the  tides  are  in  reality  very  long,  low  waves;  but 
while  the  surf  caused  by  the"  arrival  of  successive  swells  may  roll  in 
on  a  beach  every  five  or  ten  seconds,  the  high  tide  rolls  in  only  every 
12  hours  26  minutes.  Its  strength  is  usually  less  On  headlands  than 
in  bay  heads. 


THE  OCEAN  127 


QUESTIONS 

Secs.  68,  69.  What  is  the  ocean?  Compare  the  Arctic  and  Ant- 
arctic oceans.  Locate  the  poles  of  the  land  and  water  hemispheres. 
Cpnsider  the  ocean  as  a  highway. 

70,  71.  Compare  the  earlier  and  later  objects  of  ocean  exploration. 
Describe  the  method  of  deep  sounding.  What  is  a  water  bottle  V  a 
dredge  V  How  are  nets  used  in  sounding  ?  Where  are  the  places  of 
greatest  depth  in  the  ocean  ?     About  how  deep  are  they  ? 

72,  73.  What  mineral  substances  are  dissolved  in  ocean  water? 
What  is  their  source?  What  gases  are  dissolved  in  ocean  water? 
What  purpose  does  one  of  these  gases  serve?  What  is  the  density 
of  ocean  water  ?  What  amount  of  dissolved  substances  does  it  con- 
tain ?  Compare  the  ocean  and  the  atmosphere.  Describe  the  colors  of 
the  ocean  under  different  conditions.    What  causes  phosphorescence  ? 

74.  Describe  the  distribution  of  temperature  at  the  ocean  surface ; 
at  the  ocean  bottom.  How  do  ocean  temperatures  vary  through  the 
year?  How  deep  does  sunshine  penetrate  the  ocean?  Compare  the 
effect  of  changing  temperature  on  the  density  of  fresh  water;  of 
salt  water.  How  is  the  cold  water  at  the  bottom  of  the  equatorial 
oceans  accounted  for  ? 

75.  Why  does  ice  float?  What  is  floe  ice?  pack  ice?  What  are 
icebergs  ?  What  size  do  they  reach  ?  How  do  they  float  ?  Where 
are  they  seen  ?     What  is  their  source  ? 

76.  Describe  the  deep  ocean  bottom.  What  is  the  character  and 
source  of  ocean-bottom  materials  ?  What  can  you  say  of  mountains 
and  volcanoes  in  the  ocean  ? 

77.  What  is  a  mediterranean  ?  Name  the  chief  examples.  How 
does  their  temperature  differ  from  that  of  the  oceans  ? 

78.  What  is  a  continental  shelf?  Give  some  examples.  What 
materials  are  found  on  continental  shelves?  How  are  stratified 
deposits  formed?  What  do  they  include?  How  may  they  be 
changed  to  rock?  Of  what  value  to  man  are  the  shallow  waters 
of  continental  shelves? 


128  ELEMENTARY  PHYSICAL  GEOGRAPHY 

79,  80.  What  are  waves  ?  What  size  do  they  reach  ?  How  do 
they  move  ?  Illustrate  the  difference  of  wave  movement  and  water 
movement.     What  effect  has  oil  on  waves  ? 

81,82.  What  changes  of  form  do  waves  suffer ?  What  is  swell? 
surf?  Why  does  surf  fall  forward?  What  are  "rollers"?  What 
work  is  done  by  waves  ?  To  what  depth  may  they  act  ?  What  is  an 
earthquake  wave  ?     Describe  two  examples. 

83.  What  are  ocean  currents  ?  What  is  their  general  movement  ? 
What  divisions  of  the  ocean  are  suggested  by  its  eddying  currents  ? 
What  is  a  drift?  a  stream?  Of  what  practical  importance  is  a 
knowledge  of  ocean  currents?  How  are  ocean  currents  determined? 
What  is  the  cause  of  ocean  currents  ?  How  is  this  proved  ?  Name 
and  describe  some  important  members  of  the  oceanic  eddies.  To 
what  should  the  name  Gulf  Stream  be  limited  ?  How  may  sailing 
vessels  take  advantage  of  winds  and  currents  ? 

84.  How  do  ocean  currents  influence  the  distribution  of  tempera- 
ture ?     Give  examples  from  Labrador,  Great  Britain,  Alaska,  Peru. 

85.  What  are  the  tides?  Define  high  tide,  low  tide,  slack 
water,  flood,  ebb.  How  are  tides  caused?  What  practical  bene- 
fits arise  from  them  ?  What  inconveniences  ?  What  is  tidal  range  ? 
What  may  it  amount  to  ?  Where  does  strong  range  occur  ?  What 
is  a  tidal  bore  ?  What  work  is  done  by  tidal  currents  ?  When  is  this 
work  most  effective?     What  is  a  tidal  race  ?,    Give  an  example. 

86.  Consider  the  distribution  of  life  in  the  ocean  surface  waters. 
How  is  it  chiefly  controlled?  What  is  a  sargasso  sea?  What  can 
you  say  about  the  intermediate  depths  ?  the  bottom  ?  What  can  be 
inferred  from  the  color  and  eyes  of  deep-sea  animals  ?  Consider  the 
distribution  of  life  in  the  shallow  marginal  waters. 


CHAPTER   IV 
THE   LANDS 

88.  Area  of  the  Lands.  —  The  globular  earth  is  Tineven 
enough  to  raise  somewhat  more  than  a  quarter  of  its  sur- 
face slightly  above  the  oceans  in  broad  land  areas,  called 
continents. 

The  area  of  the  globe  is  about  197,000,000  square  miles. 
The  lands  occupy  somewhat  more  than  50,000,000  square 
miles ;  their  total  area  remains  uncertain  until  the  polar 
regions  are  fully  explored.  Six  sevenths  of  the  land  area 
are  in  the  land  hemisphere  (see  Figure  34),  where  the 
ocean  occupies  little  more  than  half  the  surface.  The 
lands  in  the  water  hemisphere  occupy  only  about  one 
fifteenth  of  the  surface. 

89.  The  Continents.  —  There  are  five  large  bodies  of 
land,  known  as  continents.  Europe  and  Asia  together 
form  a  single  continent,  often  called  Eurasia,  the  largest 
of  the  five.  On  account  of  the  great  extent  of  this 
continent,  and  still  more  because  of  its  varied  relations  to 
human  history,  it  is  convenient  to  describe  both  Europe 
and  Asia  as  a  "grand  division"  of  land. 

The  other  continents  are  Africa,  North  and  South 
America,  and  Australia,  the  last  being  the  smallest  of 
the  five.     It  is  possible  that  the  lands  of  the  Antarctic 

129 


130  ELEMENTARY  PHYSICAL  GEOGRAPHY 

regions  may  be  discovered  to  be  large  enough  to  rank  as 
a  continent;   but  little  is  known  of  them  at  present. 

The  five  continents  differ  greatly  in  size,  outline, 
arrangement  of  parts,  and  degree  of  separation.  The 
most  remarkable  fact  concerning  their  distribution  over 
the  earth's  surface  is  that  they  cluster  around  the  Arctic 
circle,  inclosing  the  Arctic  ocean,  and  thence  extend  far 
southward,  narrowing  toward  their  ends  in  the  great  ocean 
of  the  southern  hemisphere.  The  narrow  North  Atlantic 
and  the  much  narrower  Bering  strait  occupy  only  about  one 
ninth  of  the  Arctic  circle;  the  rest  of  its  circuit  crosses 
the  lands,  with  a  few  narrow  arms  ofHhe  sea  that  separate 
some  of  the  Arctic  islands  from  North  America. 

South  America  lies  southward  of  North  America; 
Africa  lies  southward  of  western  Eurasia ;  Australia  lies 
southward  of  eastern  Eurasia.  None  of  these  southern 
continents  reach,  the  parallel  of  60°  south  latitude;  the 
whole  circuit  of  this  parallel  lies  on  the  ocean. 

Another  remarkable  feature  in  the  distribution  of  the 
lands  is  that  two  land  areas  are  seldom  found  opposite 
to  each  other,  on  opposite  sides  of  the  earth.  Opposed 
to  each  continent  is  generally  an  ocean  surface,  as  may  be 
seen  by  examining  a  globe. 

A  third  remarkable  feature  regarding  the  distribution 
of  the  lands  is  that,  excepting  Australia  and  the  possible 
Antarctic  continent,  nearly  all  the  other  lands  are  found 
on  one  half  of  the  earth's  surface,  known  as  the  land  hemi- 
sphere.    (See  page  96.) 

Eurasia  and  Africa  are  often  called  the  Old  World, 
because  parts  of  them  have  been  known  to  the  people  of 


THE  LANDS  131 

our  race  for  more  than  twenty  centuries  ;  while  North  and 
South  America  are  called  the  New  World,  because  they 
have  been  known  to  us  for  only  a  little  more  than  four 
centuries.  But  these  names  are  appropriate  only  from 
the  point  of  view  of  human  history.  Both  the  Old  and 
the  New  Worlds,  so  called,  contain  so  much  very  ancient 
land,  raised  above  the  ocean  in  early  stages  of  the  earth's 
history,  and  so  many  mountains  and  plains  that  have  been 
formed  in  the  later  stages  of  the  earth's  history,  that 
neither  world  should  be  regarded  as,  on  the  whole,  older 
or  younger  than  the  other. 

The  greatest  islands  are  comparatively  near  the  conti- 
nents, as  in  the  archipelago  north  of  North  America,  the 
West  Indies,  Newfoundland,  the  British  Isles,  Madagas- 
car, the  Japanese  islands,  the  Malayan-Australasian  archi- 
pelago, and  New  Zealand.  Most  of  these  islands  stand 
upon  continental  shelves  and  are  separated  from  the  con- 
tinents only  by  comparatively  shallow  water;  but  New 
Zealand  is  separated  from  Australia  by  deep  water.  The 
numerous  oceanic  islands,  distant  irom  continents,  are  of 
small  total  area  (about  40,000  square  miles). 

90.  Height  of  the  Lands. — The  highest  mountain  peaks 
(25,000  to  29,000  feet)  do  not  rise  above  sea  level  so  much 
as  the  greatest  ocean  depths  sink  below  it  (31,600  feet). 
The  average  elevation  of  the  lands  (2400  feet,  less  than 
half  a  mile)  is  much  less  than  the  average  depth  of  the 
oceans  (about  two  miles). 

Figure  58  exhibits  the  proportion  of  high  and  low  land, 
and  of  deep  and  shallow  ocean,  the  whole  area  of  the  earth 


132 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


being  measured  by  the  breadth  of  the  figure.  It  is  thus  seen 
that  most  of  the  land  surface  is  but  little  above  sea  level, 
wliile  most  of  the  sea  floor  lies  deep  below  the  sea  surface. 

91.  Changes  of  Continental  Outline.  —  The  form  of  the 
lands  and  the  outline  of  their  shores  seem  at  first  sight  to 
be  unchangeable.  But  the  more  the  world  is  studied,  the 
more  certain  it  becomes  that  very  slow  movements  are 

going  on  in  the 
earth's  crust, 
and  that  the  out- 
000  line  of  the  con- 
tinents is  sub- 
ject to  change 
as  the  conti- 
nental masses 
very  slowly  rise 
or  sink.  The 
movements  are 
so  slow  that 
they  are  hardly  perceptible  in  the  course  of  a  century; 
but  when  continued  for  hundreds  of  centuries  they  cause 
changes  of  great  importance  in  the  geography  of  the  lands. 
Observations  in  the  last  hundred  years  or  more  give 
reason  to  believe  that  the  coasts  of  Massachusetts  and 
New  Jersey  are  now  sinking  (one  or  two  feet  a  century), 
and  that  much  of  the  coast  of  Sweden  is  rising  (greatest 
rise,  three  feet  a  century).  The  coast  of  the  Netherlands 
is  sinking  a  foot  a  century,  and  its  fields  near  the  shore, 
fifteen  to  twenty  feet  below  the  sea  level,  are  diked  to  keep 


80,000 


80,000 


Fig.  58.    Height  of  Land  and  Depth  of  Sea 


THE  LANDS  133 

the  water  off.  Canada  northeast  of  the  Great  lakes  is 
rising,  so  that  the  waters  of  the  lakes  are  slowly  backing 
up  on  their  southwestern  shores. 

Widespread  layers  of  rock  containing  fossils  of  sea 
animals  are  found  on  various  parts  of  the  continents,  show- 
ing that  these  parts  of  the  lands  have,  in  some  ancient 
time,  been  beneath  the  sea.  Many  other  proofs  of  change 
of  level  will  be  given  on  later  pages. 

92.  Varied  Conditions  on  the  Land  Surface. — The  sur- 
face of  the  continents  possesses  great  variety  of  form  and 
composition,  very  unlike  the  monotony  of  the  broad  and 
deep  sea  floors.  Rocks  and  soils,  as  well  as  mountains, 
valleys,  and  plains,  differ  greatly  from  place  to  place. 

Mountain  ranges  are  characteristic  of  the  continents 
rather  than  of  the  sea  floors,  where  plains  of  vast  extent 
prevail.  But  mountain  ranges  occasionally  rise  from  the 
sea  bottom,  showing  their  crests  above  the  surface,  as  in 
the  West  Indies.  Volcanoes  and  their  lavas  are  among 
the  few  features  possessed  in  common  by  the  deep  sea 
and  the  dry  lands. 

The  continental  shelves,  overlapped  by  some  of  the 
oceans,  have  something  of  the  variety  of  the  lands  from 
which  they  receive  washings  of  gravel,  sand,  and  clay. 

While  the  deep-sea  floor  is  always  wet,  dark,  cold,  and 
quiet,  the  land  surface  has  many  different  kinds  of  weather 
and  climate.  Heavy  rains  are  followed  by  clear  sky; 
strong  winds,  by  light  winds  or  calms.  A  bare  desert 
surface  in  the  torrid  zone  may  be  heated  at  noon  above 
130°,  and  may  cool  nearly  to  freezing  the  next  night.     In 


134  ELEMENTARY  PHYSICAL  GEOGRAPHY 

the  frigid  zone  the  frozen  soil  may  warm  and  thaw  at  the 
surface  during  summer,  but  it  will  be  frozen  again,  even 
to  80°  below  zero,  the  next  winter. 

Variations  of  temperature,  so  distinct  on  the  land  sur- 
face, rapidly  decrease  underground.  At  a  depth  of  four 
or  five  feet  daily  changes  are  hardly  perceptible  ;  at  a  depth 
of  twenty  or  thirty  feet  there  is  but  little  variation  from 
the  mean  temperature  of  the  year  (about  80°  in  the  torrid 
zone,  near  zero  in  far  northern  lands). 

In  northeastern  Siberia,  where  the  ground  is  frozen  to  a 
depth  of  300  to  500  feet,  grass  and  bushes  grow  when  the 
soil  thaws  for  a  few  feet  in  summer;  but  large  trees  are 
wanting.  The  mammoth,  an  ancient  animal  resembling  a 
hairy  elephant,  but  no  longer  found  living,  has  on  account 
of  the  extreme  cold  sometimes  been  preserved  in  the  beds 
of  sand  and  gravel  that  border  some  of  the  Siberian  rivers, 
where  it  was  buried  at  the  time  of  river  floods  many 
centuries  ago,  and  afterward  frozen. 

93.  Activities,  of  the  Lands.  —  In  nothing  do  the  conti- 
nents differ  more  strikingly  from  the  deep-sea  floors  than 
in  the  activity  of  the  various  processes  that  go  on  upon 
the  lands,  and  in  the  changes  that  the  processes  produce. 
The  surface  rocks  split  apart  when  water  freezes  in  their 
crevices,  or  they  slowly  rust  and  decay  under  the  action 
of  air  and  water.  A  sheet  of  loosened  rock  waste  is 
thus  formed  over  most  of  the  land  surface.  The  various 
processes  by  which  rock  waste  is  produced  are  known 
under  the  general  term  weathering.  Weathering  varies 
greatly  under  different  climates  and  with  different  rocks. 


THE  LANDS 


135 


Every  rock-ledge  or  quarry  offers  opportunity  for  observ- 
ing the  widespread  process  of  weathering.  The  weathering 
of  the  older  gravestones  in  cemeteries  may  frequently  be 
noticed.  In  cities  the  different  amounts  of  weathering  on 
old  and  new  stone  buildings,  or  in  buildings  of  different 
kinds  of  stone,  serve  to  illustrate  in  a  simple  way  the 
changes  that  occur  on 
a  much  greater  scale 
all  over  the  lands. 

In  the  dry,  mild, 
and  equable  climate 
of  Egypt  ancient 
statues  have  been  but 
slightly  weathered  in 
several  thousand 
years.  A  great  stone 
monument,  sixty  feet 
high,  known  as  Cleo- 
patra's  Needle, 
brought  from  Egypt 
to  New  York  in  1880,  was  so  much  affected  by  the  weather 
in  a  single  winter  that  it  became  necessary  to  coat  its  sur- 
face with  a  preservative  substance.  In  Egypt  it  had  stood 
over  3000  years  with  little  change. 

In  regions  of  plentiful  rainfall  and  abundant  vegetation 
weathering  advances  with  comparative  rapidity,  and  a  deep 
soil  is  formed;  solid  rock  may  not  be  found  for  fifty  or  more 
feet  below  the  surface.  In  high  latitudes,  where  the  tem- 
perature frequently  rises  and  falls  past  the  freezing  point, 
frost  is  active  in  splitting  rock  masses  into  fragments. 


Fig.  59.    A  Quarry  showing  Weathered  Rock 


136  ELEMENTARY  PHYSICAL  GEOGRAPHY 

94.  The  Wasting  of  the  Lands.  — Surface  water,  supplied 
by  rain  or  melting  snow,  washes  the  finer  rock  waste  down 
the  slope  of  the  land  to  th-e  valley  floors  or  to  the  streams, 
and  the  streams  bear  the  waste  along  their  channels,  thus 
sweeping  it  from  one  place  and  spreading  it  over  another, 
or  washing  it  to  the  sea.  Where  streams  run  they  rasp 
their  channels  with  the  rock  grains  that  they  bear  along, 
and  valleys  are  thus  slowly  worn  in  the  surface  of  the  land. 
The  higher  the  land,  the  deeper  the  valleys  may  be  cut. 

The  longer  the  period  of  wasting  and  washing,  the  more 
material  is  taken  from  the  valley  sides  and  the  wider  and 
more  open  the  valleys  become. 

Large  valleys,  receiving  many  smaller  branching  valleys 
and  ravines  that  dissect  the  surface  of  the  land  and  lead 
streams  from  higher  to  lower  ground,  are  among  the  most 
characteristic  features  of  the  continents.  Valleys  are  the 
result  of  stream  action  and  do  not  occur  on  the  deep-sea 
floor.  They  are  sometimes  found  beneath  sea  level,  extend- 
ing forward  from  the  present  coast  line  across  the  shallow 
continental  shelf;  they  are  then  taken  as  proof  of  the 
lowering  of  that  part  of  the  continent. 

The  winds  act  with  great  effect  on  bare  surfaces,  sweep- 
ing finer  rock  waste  into  drifts  (dunes),  and  raising  the 
dust  aloft  to  settle  far  away.  The  waves,  currents,  and 
tides  of  the  ocean  wear  the  edge  of  the  land  and  the 
shallow  continental  margins,  cutting  cliffs  and  building 
sand  reefs  along  the  shores,  and  sweeping  away  the  finer 
land  waste. 

The  general  process  of  wasting  and  washing,  by  which 
the  land  surface  is  slowly  worn  down  and  the  deeper 


THE  LANDS  137 

structures  of  the  earth's  crust  are  attacked,  is  called  denu- 
dation or  erosion.  The  movement  of  land  waste  from  one 
place  to  another  by  various  agents  (streams,  currents, 
winds,  waves,  etc.)  is  called  transportation.  The  process 
of  laying  down  land  waste  on  valley  floors,  in  lake  basins, 
and  on  sea  floors  is  called  deposition. 

Illustrations  of  these  various  processes  may  be  found 
on  a  small  scale  in  the  neighborhood  of  many  schools. 
The  wet-weather  streams  of  roadsides  and  the  waves  in 
ponds  or  reservoirs  exhibit  in  a  small  way  the  processes  of 
erosion  and  transportation  in  large  rivers  and  oceans.  The 
sjrong  action  of  winds  on  dusty  roads  and  their  lack  of 
effect  on  the  ground  beneath  grass  or  forests  illustrate  the 
contrast  that  prevails  between  wind  action  in  dry  and  in 
moist  regions. 

The  difference  between  the  conditions  that  prevail  on 
the  land  surface  and  on  the  sea  floor  is  thus  seen  to  be 
very  great.  The  sea  floor  is  enduringly  quiet  and  silent. 
The  tides  of  the  deep  sea  are  very  faint.  The  creeping 
of  cold  polar  water  toward  the  equator  must  be  almost 
imperceptible.  The  gain  of  the  bottom  by  the  steady 
shower  of  organic  remains  from  the  surface  is  very  feeble, 
and  the  change  of  form  by  this  gain  must  be  exceedingly 
slow. 

Although  the  changes  caused  in  the  form  of  the  lands 
by  weathering  and  washing  are  gradual,  they  have  been  so 
long  continued  that  marvelous  results  have  been  produced. 
Not  only  are  the  lands  deeply  dissected  where  valleys  have 
been  worn  in  plateaus  and  mountains,  but  whole  mountain 
ranges  have  been  worn  down  to  lowlands.     The  forms  of 


138  ELEMENTARY  PHYSICAL  GEOGRAPHY 

the  land  to-day  can  be  appreciated  only  when  it  is  seen 
that  they  are  the  present  stage  of  a  long  series  of  changes. 
The  description  and  explanation  of  land  forms  thus  con- 
sidered is  the  object  of  most  of  the  remainder  of  this  book. 

The  general  wasting  of  a  land  surface  is  slow,  but  local 
changes  are  easily  noted  by  the  attentive  observer.  Slop- 
ing fields  and  roads  are  gullied  by  wet-weather  streams. 
Much  soil  may  be  washed  from  a  plowed  hillside  in  a 
single  rain  storm.  Landslides  produce  striking  changes 
on  mountain  slopes  and  in  the  valleys  below.  Cataracts 
like  Niagara  wear  back  their  cliffs  more  than  a  foot  a 
year. 

The  land  waste  that  is  washed  down  a  valley  is  deposited 
at  the  mouth  of  the  stream  in  a  lake  or  the  sea,  and  thus 
the  land  is  built  out,  forming  a  delta,  which  may  grow 
forward  perceptibly  in  a  century.  Ostia,  once  the  port  of 
ancient  Rome,  is  now  over  a  mile  inland  from  the  advanc- 
ing front  of  the  Tiber  delta.  Sea  cliffs  may  be  cut  back 
by  the  waves ;  part  of  the  exposed  eastern  bluff  of  Cape 
Cod,  Massachusetts,  is  retreating  at  an  average  rate  of 
thi'ee  feet  a  year. 

The  rate  of  erosion  on  the  lands  varies  greatly  with  rock 
structure,  slope,  and  climate.  The  Mississippi  carries 
enough  land  waste  to  lower  its  whole  basin  an  inch  in  about 
three  centuries.  An  inch  in  from  one  to  ten  centuries 
may  be  taken  as  a  rough  measure  of  erosion,  averaged 
for  large  areas. 

95.  Useful  Products  of  the  Lands.  —  The  rock  of  the 
earth's  crust  in  the  lands  is  of  great  service  in  building  and 


'     THE  LANDS  139 

road  making ;  hence  it  is  often  quarried.  Clay  is  burned 
to  make  bricks,  used  in  building  and  street  paving.  Lime- 
stone when  heated  ("  burned  ")  is  changed  to  lime,  used 
in  making  mortar.  Coal,  found  in  layers  between  strata 
of  clays  and  sandstones,  is  the  most  useful  kind  of  fuel. 
Rock  oil,  or  petroleum,  is  of  great  value  as  a  fuel  for 
lamps,  and  in  many  other  ways.  The  ores  of  many  metals 
are  mined  and  smelted,  to  supply  man's  needs ;  iron,  copper, 
lead,  tin,  and  zinc  are  the  most  useful  metals  in  manufac- 
tures ;  gold  and  silver  are  used  as  money  and  in  the  arts. 
Precious  stones  or  gems,  such  as  the  diamond,  ruby,  and 
emerald,  are  highly  prized  for  their  beauty  and  rarity. 

All  these  products  of  the  lands  play  an  important  part 
in  the  advance  of  civilization.  Spain  has  iron  ore  but  no 
coal.  England  has  abundant  coal  and  iron  ore.  How  is 
the  present  condition  of  these  two  countries  affected  by 
the  presence  and  absence  of  coal  supply?  The  United 
States  possesses  extensive  coal  fields  and  abundant  deposits 
of  iron  ore,  as  well  as  other  mineral  products  in  great 
variety.  Argentina  possesses  relatively  little  mineral 
wealth.  What  other  comparisons  can  you  make  between 
these  two  countries  ? 

QUESTIONS 

Secs.  88,  89,  90.  What  is  the  area  of  the  globe  ?  of  the  lands  ? 
State  three  remarkable  facts  concerning  the  distribution  of  the 
lands.  Why  are  the  terms  Old  World  and  New  World  not  appro- 
priate in  physical  geography?  State  the  relation  of  the  larger 
islands  to  the  continents.  Compare  land  heights  and  ocean  depths. 
State  the  proportion  of  high  land  to  deep  ocean. 


140  ELEMENTARY  PHYSICAL  GEOGRAPHY 

91.  What  changes  are  taking  place  in  continental  outline?  Give 
some  examples. 

92.  Contrast  the  land  surface  and  the  sea  floor  as  to  form ;  as 
to  changes  of  temperature.  Contrast  the  distribution  of  mountain 
chains  and  of  volcanoes.  How  does  temperature  vary  underground? 
Describe  the  effects  of  extreme  cold  in  northeastern  Siberia. 

93.  What  changes  take  place  on  the  lands?  What  is  weather- 
ing? Give  examples  of  it.  Name  some  of  its  effects.  How  does 
frost  act  and  where  is  it  most  effective  ? 

94.  Describe  the  action  of  streams.  How  are  the  depth  and 
width  of  valleys  determined?  Why  are  valleys  characteristic  of  the 
lands?  How  are  the  lands  affected  by  the  winds?  by  waves  and 
tides?  Define  denudation.  What  effects  of  erosion  have  you  seen? 
State  the  effects  of  long-continued  erosion.  What  changes  have 
occurred  on  shore  lines  ?  Upon  what  does  the.  rate  of  erosion 
depend?    What  is  its  average  rate? 

95 .  What  are  some  of  the  useful  products  of  the  earth's  crust  ? 
What  comparison  can  yoa  make  between  England  and  Spain? 
between  the  United  States  and  Argentina? 


CHAPTER   V 

PLAINS  AND  PLATEAUS 

96.  Introductory  Example.  —  In  certain  parts  of  the 
world  the  hills  bordering  a  mountain  range  descend  directly 
to  the  seashore.  Rock  waste  is  washed  from  the  moun- 
tain slopes  and  carried  down  the  valleys  by  streams.  The 
larger  rivers  build  deltas  at  their  mouths,  and  here  the  sea 
is  bordered  by  low  land.  Waves  beat  on  the  coast  and 
cut  cliffs  in  the  headlands  between  the  valleys;  here  the 
sea  is  bordered  by  high  land.  The  waste  of  the  land  is 
spread  over  the  neighboring  sea  floor  by  waves  and  currents. 

Figure  60  is  a  picture  of  a  model  representing  a  region 
of  this  kind.  Moiuitains  and  ridges  of  varied  form  descend 
toward  the  shore  line.  A  river  in  a  large  central  valley 
receives  the  streams  with  their  rock  waste  from  a  number 
of  branching  valleys  and  has  built  a  delta  at  its  mouth. 
This  means  that  while  the  land  has  been  eroded  and 
roughened  by  the  action  of  weather  and  streams  the  sea 
floor  has  been  smoothed  by  the  gain  of  land  waste.  The 
depth  and  number  of  the  valleys  show  that  already  much 
waste  has  been  carried  into  the  neighboring  sea.  The 
dredge  brings  up  gravel,  sand,  and  mud  from  the  sea  bot- 
tom, the  sediments  usually  being  of  finer  grain  as  distance 
from  l^md  and  depth  of  water  increase. 

141 


142 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Figure  61  is  a  map  of  part  of  the  mountains  shown  in  Figure  60. 
The  form  of  the  ridges  is  here  indicated  by  short  lines,  called  hachure 


^ ill 


Fig.  60.    Mountains  bordering  the  Sea 


lines,  which  show  the  direction  in  which  the  slopes  descend.     Gentle 
slopes  may  be  represented  by  long  fine  lines,  steep  slopes  by  short 
heavier  lines.     This  map  may  serve  as  a  sample  for  a  number  of  others 
that  should  be  drawn  from  the 
figures  on  later  pages. 


A  rugged  land  like  that 
of  Figure  60  seldom  sup- 
ports a  large  population, 
for  it  is  not  easy  to  gain 
a  living  on  steep  moun- 
tain sides.  It  is  only  in 
the  valleys  that  strips  of 
flat  land,  suitable  for  easy 
occupation,  can  be  found. 
Most  of  the  population  in 
such  a  region  is  gathered 


Fig.  61. 


Sample  Map  of  a  Mountainous 
Coast 


LAINS  AND  PLATEAUS  143 

in  villages  near  the  mouths  of  the  large  rivers,  where  the 
valleys  are  wider  and  the  ridges  between  them  are  lower. 
Roads  cannot  easily  follow  the  shore,  for  many  of  the  cliffs 
are  washed  to  their  base  at  every  high  tide.  In  passing 
from  one  valley  village  to  another  the  traveler  must  climb 
over  a  ridge;  this  is  hard  work  and  it  discourages  settle- 
ment. Many  dwellers  in  the  shore  villages  are  seafarers 
and  fishermen,  although  there  are  few  protected  harbors, 
for  the  shore  line  is  comparatively  straight. 

The  coast  of  California  presents  many  stretches  of  this 
kind.  The  Sierra  Santa  Lucia,  south  of  Monterey,  descends 
boldly  to  the  sea,  its  spurs  being  cut  off  in  great  cliffs. 
The  shore  is  harborless  and  thinly  inhabited  for  a  distance 
of  seventy  miles. 

97.  Narrow  Coastal  Plains.  —  There  are  some  regions 
where  the  foothills  of  the  mountains  descend  to  a  lowland, 
and  the  lowland  slopes  gently  forward  to  the  sea.  Such  a 
lowland  is  called  a  coastal  plain.  The  gentle  slope  of  the 
lowland  is  continued  in  the  slowly  deepening  sea  floor. 
The  form  of  the  land  is  here  much  more  favorable  to 
human  occupation  than  in  the  previous  example. 

Plains  of  this  kind  are  often  divided  into  many  simi- 
lar strips  by  the  shallow  valleys  of  streams  that  flow 
across  them  from  the  mountains.  Each  strip  of  the  plain 
is  so  smooth  and  so  nearly  level  that  a  great  part  of  the 
rainfall  enters  the  open  soil,  instead  of  running  off  in 
streams.  The  plain  is  built  of  layers  or  strata  of  gravel, 
sand,  and  clay,  the  uppermost  layer  or  stratum  forming 
the  surface  of  the  plain.    The  pebbles  of  the  gravel  often 


144 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


resemble  the  harder  rocks  of  the  hilly  background;  the 
clay  often  contains  shells  like  those  living  in  the  sea. 
Figure  62  shows  a  region  of  this  kind. 

Trace  the  line  between  the  mountains  and  the  coastal  plain  in 
Figure  62.  How  many  streams  are  seen  crossing  the  plain?  Which 
stream  has  the  broadest  valley?  Why?  Compare  the  depth  of  the 
valleys  in  the  plain  with  that  of  the  valleys  in  the  mountains. 


Fia.  62.    Narrow  Coastal  Plain 


Draw  a  map  to  represent  part  of  the  coastal  plain  of  Figure  62 
and  some  of  the  hills  bordering  its  inner  margin.  Notice  that  in 
the  figure  the  streams  crossing  the  plain  are  foreshortened,  while 
the  spaces  between  the  streams  are  on  true  scale.  Figure  63  illus- 
trates the  way  in  which  the  map  should  be  drawn. 

Little  ravines  have  been  eroded  by  we1>-weather  streams 
in  the  side  slopes  of  the  plain  bordering  the  valleys.  Even 
the  larger  valleys  have  been  slowly  eroded  by  the  rivers 
that  flow  through  them.     In  the  future  the  plain  will  be 


PLAINS  AND  PLATEAUS 


145 


more  carved  or  dissected ;  iii  the  past  it  was  less  dissected. 
Before  any  valleys  were  cut  the  different  parts  of  the  plain 
were  all  united  in  a  continuous,  even  surface. 

In  view  of  all  this,  it  must  be  concluded  that  the  coastal 
plain  in  Figure  62  was  once  part  of  a  shallow  sea  bottom 
and  that  this  region  was 
then  like  the  sea-skirted 
mountains  of  Figure  60. 
Since  then  the  relative 
level  of  the  land  and  sea 
must  have  been  altered, 
laying  bare  a  part  of  the 
smoothed  sea  bottom  to 
form  the  coastal  plain. 

As  the  region  now 
stands  higher  than  before, 
the  rivers  tend  to  wear 
down  their  valleys  to  the 
new  level  of  the  sea  at 
their  mouths;  the  valley 
sides  waste  away,  and 
thus  the  valleys  slowly 
become    wider;    but    the 

streams  cannot  wear  the  valleys  deeper  than  the  surface 
of  the  sea  at  their  mouths.  The  level  of  the  sea  is  there- 
fore called  the  haselevel  of  the  region. 

Slender  belts  of  a  very  narrow  coastal  plain,  less  than  a 
mile  wide,  are  found  along  parts  of  the  western  coast  of  Scot- 
land; they  are  even  narrower  than  the  plain  represented 
in  Figure  62,  being  wide  enough  for  only  a  single  row  of 


Fig.  63. 


Sample  Map  of  a  Narrow 
Coastal  Plain 


146  ELEMENTARY  PHYSICAL  GEOGRAPHY 

fields.  The  houses  of  the  farmers  are  generally  placed 
near  the  inner  margin  of  the  plain;  a  few  fields  are  cleared 
on  the  lower  slopes  of  the  back  country;  cattle  pasture 
on  the  higher  hillsides ;  the  cultivated  crops  are  gathered 
chiefly  from  the  smooth  surface  of  the  little  plain. 


Fig.  Gi.     A  Narrow  Coastal  Plain  in  Scotland 

A  number  of  narrow  and  low  coastal  plains  occur  along 
the  coast  of  Oregon.  They  are  one  or  two  miles  wide  and 
twenty  or  more  miles  long.  Heavily  forested  mountains 
rise  in  the  background,  too  uneven  for  easy  occupation; 
but  the  even  surface  and  gentle  slope  of  the  coastal  plains 
make  them  attractive  to  settlement,  although  they  suffer 
the  disadvantage  of  having  no  good  harbors. 

The  eastern  coast  of  Mexico  in  the  neighborhood  of  Vera 
Cruz  is  bordered  by  a  low  coastal  plain  about  fifty  miles 


PLAINS  AND  PLATEAUS  147 

wide,  back  of  which  tlie  mountains  rise  rather  abruptly. 
Part  of  the  plain  is  covered  with  extensive  mud  flows 
from  volcanoes  in  the  mountains.  Vera  Cruz,  the  chief 
port  for  the  interior  highlands,  has  a  poorly  protected 
anchorage  on  the  open  shore. 

98.   Broad  Coastal  Plains.  —  Figure    65    represents   a 
broader  coastal  plain  than  the  preceding  examples.     The 


Fig.  65.    Broad  Coastal  Plain 

outer  part  of  this  plain  is  much  like  the  plain  in  Figure  62 ; 
but  the  inner  part  is  more  cut  by  branching  valleys  and 
ravines,  so  that  it  presents  a  hilly  rather  than  a  plain  sur- 
face, and  the  larger  rivers  have  broader  valleys  than  before. 
The  unevenness,  or  "relief,"  of  the  surface  increases 
inward  from  the  shore  line  in  consequence  of  the  greater 
depth  to  which  the  valleys  are  cut  in  the  higher  part  of 
the  plain.  Where  the  uplands  are  much  interrupted  by 
branching  valleys  the  plain  is  said  to  be  well  dissected. 


148 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


During  the  slow  uplift  of  the  region  different  kinds  of 
sediments  may  have  been  laid  down  near  the  shore,  as  the 
sea  retired  from  the  plain.  Hence  the  soils  of  such  plains 
are  commonly  of  different  kinds  in  the  inner,  middle,  and 
outer  parts,  being  arranged  in  belts  roughly  parallel  to  the 
length  of  the  plain. 

The  Atlantic  coastal  plain  of  the  Southern  States,  of 
which  a  characteristic  portion  is  included  in  South  Caro- 
lina, Figure  66, 
is  dissected  by 
many  branch- 
ing valleys  in 
its  inner  part. 
It  may  be 
divided  into 
several  belts 
parallel  to  the 
shore  line. 
The  outer  or 
coastal  lowland 
is  a  smooth 
plain,  with  open 
pine  woods  or  grassy  savannahs ;  this  division  is  about  fifty 
miles  wide,  rising  so  gently  that  it  seems  level  to  the  eye. 
Its  surface  is  very  poorly  drained. 

The  plain  slowly  rises  inland  with  gently  rolling  sur- 
face; here  the  soil  is  better  than  in  the  first  belt,  and  much 
cotton  is  raised.  Farther  inland  still  the  surface  becomes 
more  sandy  again  and  more  hilly,  giving  extensive  views 
seaward  across  the  lower  plain.     A  hundred  miles  inland 


Fig.  66.    Coastal  Plain  of  the  Carolinas 


PLAINS  AND  PLATEAUS 


149 


a  belt  of  hilly  uplands  stands  600  or  700  feet  above  the 
sea,  covered  with  pine  forests.  Here  the  plain  is  well  dis- 
sected, its  original  surface  being  almost  entirely  destroyed 
by  the  action  of  many  streams  in  carving  their  valleys  and 
by  the  action  of  the  weather  in  opening  the  valley  slopes. 
Then  come  the  hills  of  the  older  land  (the  Piedmont 
belt,  here  not  moimtainous,  but  of  moderate  relief),  whence 


Fia.  67.  A  Truck  Farm  on  the  North  Carolina  Coastal  Plain 


the  strata  of  the  plain  have  received  their  sediments,  and 
where  the  rivers  are  now  cutting  down  narrow  valleys 
beneath  their  former  valley  floors. 

The  soil  belts  on  this  plain  exert  an  important  control  over 
the  industries  of  the  people.  The  less  sandy  soils  are  occu- 
pied by  cotton  plantations.  Extensive  pine  forests  on  the 
more  sandy  belts  furnish  much  lumber,  tar,  and  turpentine. 


150 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


The  moist  swampy  soils  near  the  coast  are  well  adapted 
to  the  cultivation  of  rice.  The  more  limy  layers  of  the 
plain  are  dug  up  to  fertilize  the  more  sandy  fields,  and  the 
richest  of  these  limy  deposits  are  exported  to  other  states 
to  be  used  as  fertilizers.  In  North  Carolina  numerous 
farms  on  the  coastal  plain  furnish  vegetables  for  the  mar- 
kets of  northern  cities. 

99.  Belted  Coastal  Plains. —  Figure  68  exhibits  a  coastal 
plain  which  may  be  divided  into  three  belts  parallel  to  the 


Fig.  68.    A  Belted  Coastal  Plain 


shore  line,  each  one  ten,  twenty,  or  more  miles  wide  ;  the 
innermost  (A)  is  a  lowland ;  the  middle  belt  (B)  is  an 
upland  of  stronger  rock  layers,  several  hundred  feet  above 
the  lowland  ;  the  outer  belt  (C)  is  a  smooth  coastal  low- 
land. The  several  belts  recall  the  beltlike  arrangement  of 
soils  described  in  the  case  of  a  broad  coastal  plain,  but 
here  the  middle  belt  forms  an  upland  that  runs  about 


PLAINS  AND  PLATEAUS 


151 


parallel  to  the  shore  line  and  stands  between  an  inner 
and  an  outer  lowland.  The  upland  descends  by  a  rather 
steep  slope  to  the  inner  lowland,  and  by  a  long,  gentle, 
outlooking  slope  to  the  coastal  lowland.^ 


In  Figure  68  the  front 
of  the  diagram  is  drawn 
to  represent  what  would 
be  seen  on  the  side  of  a 
very  deep  cut  that  might 
be  imagined  to  cross  the 
plain.  The  layers  of 
clays,  sandstones,  and 
other  strata  that  form 
the  plain  are  thus  shown, 
gently  slanting  under  the 
sea.  Where  is  the  upper- 
most layer  of  the  series, 
that  is,  the  layer  that  was 
last  deposited  ?  What 
part  of  the  belted  plain 
does  it  cover?  Where  are 
the  under  layers  (the  first 
deposited)?  Where  do 
they  reach  the  present 
surface  of  the  belted 
plain  ?  Which  layers 
reach  the  surface  of  the  upland  part  of  the  belted  plain? 

Draw  an  outline  map  of  the  district  shown  in  Figure  68.  A 
sample  of  part  of  it  is  shown  in  Figure  69.  Note  that  some  small 
streams  must  run   inland,  down  the  inner   slope   of  the   upland. 


Fig.  I 


Sample  Map  of  Part  of  a  Belted 
Coastal  Plain 


1  An  upland  of  this  kind  may  be  called  a  cuesta,  following  a  word  of 
Spanish  origin  used  in  New  Mexico  for  low  ridges  of  steep  descent  on  one 
side  and  gentle  slope  on  the  other. 


152  ELEMENTARY  PHYSICAL  GEOGRAPHY 

Compare  the  arrangement  of  the  rivers  and  streams  with  those 
shown  in  the  map,  Figure  63,  drawn  from  Figure  62. 

The  reason  for  the  arrangement  of  upland  and  lowland 
may  now  be  understood.  The  under  layers  of  this  coastal 
plain  are  weaker  than  the  middle  layers ;  hence  the  under 
layers,  which  reach  the  surface  of  the  plain  near  its  inner 
border,  are  already  worn  down  to  a  lowland,  while  the  more 
resistant  middle  layers  still  preserve  an  upland  height. 

Trace  the  river  first  seen  at  Z>,  Figure  68,  and  describe  the  several 
belts  of  country  that  it  crosses  on  the  way  to  the  sea.  Where  is  its 
valley  deep  ?  where  shallow  ? 

A  good  example  of  this  kind  of  coastal  plain  is  found 
in  southern  New  Jersey,  Figure  70.  The  Delaware  river 
below  Trenton  runs  along  the  inner  lowland.  Here  is  a 
belt  of  pottery  clays,  of  which  much  crockery  and  earthen- 
ware are  made.  Then  comes  a  belt  of  farming  country 
on  rolling  hilly  ground,  which  contains  layers  of  marl 
(limy  clay);  the  marl  is  dug  to  serve  as  a  fertilizer  on  less 
productive  soils.  The  hills  rise  to  an  upland  that  descends 
in  a  long  gentle  slope  southeastward  to  a  lowland  plain 
by  the  sea ;  its  soil  is  sandy  and  its  even  surface  is  gen- 
erally overgrown  with  pine  forests.  Short  arms  of  the 
sea  enter  the  lower  valleys,  giving  harborage  for  small 
vessels ;  many  fishermen  live  in  the  shore  villages.  A 
belt  of  shallow  salt-water  lagoons  with  extensive  marshes 
of  reeds  borders  the  mainland  for  a  breadth  of  about  five 
miles.  Finally  come  the  sand  reefs,  half  a  mile  or  more 
wide,  inclosing  the  lagoons.  The  reefs  are  interrupted  by 
inlets,  connecting  the  lagoons  with  the  sea. 


PLAINS  AND  PLATEAUS 


153 


Name  the  direction  of  the  Delaware  and  the .  Schuylkill  as  they 
flow  into  the  inner  lowland ;  of  the  Delaware  in  the  inner  lowland ; 
of  the  streams  that  flow  down  the  inner  slope  of  the  cuesta  and 


Fig.  70.    Ihe  Belted  Coastal  Plain  of  Southern  New  Jersey 


across  the  marl  belt;  of  the  streams  on  the  outer  slope  of  the 
cuesta.  Which  is  the  steeper  slope  of  the  cuesta?  How  is  this 
known  ?  Compare  the  arrangement  of  all  these  streams  with  those 
shown  in  Figure  68. 

What  is  the  average  breadth  of  the  clay  belt  ?  of  the  marl  belt  ? 
of  the  hilly  belt?  of  the  sandy  plains?  of  the  coastal  lowland? 
How  far  is  it  from  Philadelphia  to  Atlantic  City? 


154  ELEMENTARY  PHYSICAL  GEOGRAPHY 

100.  Embayed  Coastal  Plains.  —  The  region  here  figured 
does  not  at  first  sight  seem  to  belong  to  the  family  of 
coastal  plains.  Long  shallow  arms  of  the  sea  enter 
between  low  hilly  arms  of  the  land.  Rivers  from  the 
back  country  enter  the  heads  of  the  long  bays ;  small 
streams  from  every  little  valley  between  the  hills  of  the 


Fig.  71.    An  Embayed  Coastal  Plain 

land  arms  enter  little  bays  or  coves  on  the  sides  of  the 
larger  bays. 

This  diagram  represents  a  coastal  plain  which  has  been 
depressed,  so  that  its  valley  floors  are  "  drowned  "  beneath 
the  sea.  Before  drowning,  the  region  must  have  stood 
for  a  long  time  higher  above  baselevel  than  now,  for  the 
valleys  evidently  had  been  eroded  and  widely  opened  before 
the  depression  of  the  region  occurred.  Many  side  valleys 
had  been  formed,  so  that  the  uplands  between  the  larger 
rivers  had  been  dissected  into  branching  spurs.  Now  the 
outer  coastal  lowland  and  the  broad  valley  floors  are  under 


PLAINS  AND  PLATEAUS 


155 


water,  the  latter  being  occupied  by  the  bays  that  enter  far 
toward  the  oldland,  while  the  groups  of  hills  stand  forth 
as  ragged  arms  of  the  land.  The  former  simple  shore  line 
is  thus  exchanged  for  a  very 
irregular  shore  line. 

Draw  a  map  of  part  of  the  em- 
bayed coastal  plain  shown  in  Fig- 
ure 71,  after  the  style  of  the  outline 
in  Figure  72.  Compare  Figures  65 
and  71.  Point  out  the  inner  border 
of  the  coastal  plain  in  each  one.  In 
what  respects  do  the  two  figures 
agree?  In  what  do  they  differ? 
How  has  the  difference  been  pro- 
duced? In  each  one  trace  a  river 
from  the  oldland  to  its  mouth. 
What  difference  is  noted? 

The  relative  change  in  the 
attitude  of  land  and  sea  is  here 
opposite  to  that  inferred  in  the 
previous   examples.      Since 
the  depression  of  the  region  the 
land  heads  have  been  more  or 
less  cut  back  by  the  waves,  and 
the  bay  heads  have  been  some- 
what filled  by  marshy  deltas.     But  the  drowning  cannot 
have  taken -place  long  ago,  as  the  earth  counts  time,  for 
the   changes  in   the   land  heads    and  bay  heads   are    of 
moderate  amount. 

The  Atlantic  coastal  plain  from  Delaware  bay  to  Pamlico 
sound  presents  many  examples  that  fall  under  this  class. 


Fig.  72.    Sample  Map  of  an  Em- 
bayed Coastal  Plain 


156  ELEMENTARY  PHYSICAL  GEOGRAPHY 

The  outer  shore  line  is  for  the  most  part  a  sand  reef, 
inclosing  lagoons.  Many  branching  bays  extend  inland, 
the  largest  being  Chesapeake  bay.  Navigable  arms  of 
the  sea  thus  alternate  with  dissected  arms  of  the  land. 

Partly  drowned  coastal  plains  exert  a  peculiar  control 
over  the  distribution  and  occupation  of  their  population. 
The  greater  part  of  the  valley  lowlands  is  lost,  and  the 
people  must  make  the  most  of  the  hilly  land  arms  that 
remain  above  sea  level.  The  axis  of  each  of  the  larger 
arms  is  generally  followed  by  a  main  road,  making  its  way 
from  village  to  village  among  the  upland  farms  and  giv- 
ing forth  side  roads  to  villages  on  the  smaller  land  arms 
or  at  the  little  bay  heads.  Indicate  the  place  of  such 
roads  and  villages  on  Figures  71   and  72. 

The  shallow  bays  are  valuable  for  fishing  grounds. 
More  important  centers  of  population  are  found  either 
near  the  heads  of  the  larger  bays,  where  the  large  rivers 
come  out  from  the  back  country  and  reach  tide  water,  or 
near  the  mouths  of  the  bays  where  the  outer  sand  reefs 
are  not  continuous  and  the  ocean  is  easily  reached. 
Baltimore  and  Norfolk  are  good  examples  of  cities  thus 
situated.  The  outer  shore  line  is  inhospitable;  its  long 
sand  reefs  offer  no  good  landing  place,  and  the  narrow 
tidal  inlets  allow  entrance  only  to  small-sized  vessels. 
Where  would  such  a  view  as  that  of  Figure  73  be  found 
in  Figure  71  ? 

In  the  early  history  of  "tide-water  Virginia"  the 
numerous  drowned  valleys  afforded  easier  communication 
between  the  settlements  than  was  found  overland  through 
the  forests  of  the  coastal  plain. 


PLAINS  AND  PLATEAUS 


157, 


101.  The  Fall  Line.  —  A  large  river  whose  valley  is 
extended  across  a  coastal  plain  often  has  low  falls  or 
rapids  near  the  inner  margin  of  the  plain,  which  determine 
the  "  head  of  navigation,"  or  uppermost  point  that  can  be 
reached  by  vessels  from  the  river  mouth.  A  line  drawn 
through  the  falls  on  successive  rivers  is  called  the  fall  line. 


Fig.  73.    A  Branch  of  Chesapeake  Bay,  Maryland 

The  falls  occur  where  the  river  passes  from  a  steeper  slope 
on  the  resistant  rocks  of  the  older  land  to  a  nearly  level 
channel  excavated  in  the  weak  strata  of  the  plain. 

On  coastal  plains  of  a  considerable  breadth  settlements 
near  the  mouth  and  at  the  head  of  navigation  of  the  larger 
rivers  often  develop  into  important  cities.  The  lower 
city  is  the  seaport  of  the  region.  The  upper  city  bears 
closer  relation  to  local  industries  and  traffic;  it  lies  in 
the  midst  of  a  diversified  region,  with  strong  water  power 
for  manufacturing  the  varied  products  of  rock  and  soil. 
In  South  Carolina,  Columbia  lies  on  the  Congaree  river, 


158  ELEMENTARY  PHYSICAL  GEOGRAPHY 

where  it  passes  from  the  older  land  to  the  dissected  plain. 
Charleston  lies  at  the  outer  edge  of  the  coastal  lowland 
on  the  widened  course  of  a  small  river  where  the  tide 
comes  in  from  the  sea. 

The  fall  line  along  the  inner  margin  of  the  Atlantic  coastal 
plain  of  the  United  States  is  marked  by  important  cities  on 
nearly  every  large  river  that  crosses  it.  Trenton,  Philadel- 
phia (at  the  falls  of  the  Schuylkill),  Richmond,  Raleigh, 
Camden,  Columbia,  and  Augusta  are  all  thus  located. 

The  origin  of  the  forces  sufficient  to  deform  the  crust 
of  the  earth  and  to  elevate  or  depress  a  coastal  plain  is  not 
well  understood.  It  is  necessary  that  the  student  of 
physical  geography  should  recognize  that  elevation  and 
depression  have  actually  taken  place,  and  should  under- 
stand the  importance  of  such  movements  in  controlling 
the  forms  of  the  lands  and  the  conditions  of  their  inhab- 
itants ;  but  the  processes  that  cause  such  movements  must 
be  left  to  the  more  advanced  study  of  geology. 

Coastal  plains,  narrow  or  broad,  belted  or  embayed,  occur 
along  parts  of  the  border  of  different  continents.  They 
resemble  more  or  less  closely  the  examples  here  given. 
The  coastal  slope  of  Guiana  and  the  plains  of  Patagonia, 
South  America,  belong  in  this  group  of  forms. 

102.  Inland  Plains.  — The  Great  plains  of  the  central 
United  States  slope  gently  forward  from  the  Rocky  moun- 
tains. They  are  formed  of  many  layers  of  sands,  clays, 
and  gravels,  washed  from  the  mountains  and  now  lying 
one  over  the  other,  many  hundred  feet  in  total  thickness 
and  nearly  horizontal.     Some  of  the  layers  were  deposited 


PLAINS  AND  PLATEAUS  169 

when  the  region  was  below  sea  level ;  some  were  spread 
over  the  uplifted  sea  bottom  by  rivers  when  the  region  was 
too  low  to  be  dissected. 

The  plains  are  now  high  enough  to  be  more  or  less 
dissected  by  streams  and  rivei-s  whose  valleys  vary  in 
depth  and  width ;  but  the  upland  spaces  between  the  val- 
leys often  preserve  a  comparatively  even  surface  over 
large  distances.  In  some  districts,  vast  areas  stretching 
farther  than  the  eye  can  reach  are  monotonously  even 
and  almost  as  uniform  in  soil  as  in  surface.  In  other  dis- 
tricts, valleys  are  deeper  and  closer  together,  and  the 
spaces  between  them  are  made  hilly  by  the  branching 
ravines  of  side  streams. 

Within  the  United  States  the  Great  plains  are  treeless 
for  500  miles  east  of  the  Rocky  mountains,  except  on 
certain  hills  and  bluffs  which  occasionally  rise  above 
the  general  level,  or  in  the  valleys  which  sink  below 
it.  The  absence  of  trees  is  due  to  the  dryness  of  the 
climate,  and  this  in  turn  is  due  to  the  general  course  of 
the  westerly  winds  whose  moisture  has  been  left  on 
the  mountain  ranges  between  the  plains  and  the  Pacific. 
Agriculture  is  impossible  in  the  drier  southern  parts 
without  irrigation.  Farther  north  in  Canada  the  climate 
is  moister,  and  the  plains  are  forested.  In  still  higher 
latitudes  the  surface  is  treeless;  the  warmth  of  summer 
melts  only  the  upper  part  of  the  soil,  and  vegetation  is  low 
and  stunted. 

The  treeless  plains  possess  little  mineral  wealth,  and  they 
have  no  forests  to  supply  lumber;  hence  they  cannot 
become  a  closely  populated  manufacturing  region ;  but  they 


160  ELEMENTARY  PHYSICAL  GEOGRAPHY 

have  a  more  or  less  abundant  growth  of  herbage,  which 
once  supported  herds  of  countless  buffaloes.  Now  that 
the  buffaloes  have  been  killed  off,  their  place  is  taken  by 
cattle  which  range  over  the  plains,  wandering  back  and 
forth  over  the  uplands  between  the  valleys  that  they  visit 
for  water.  A  number  of  railroads  traverse  the  plains  and 
carry,  among  other  things,  many  cattle  to  eastern  markets. 

The  plains  of  western  Siberia  resemble  the  Great  plains 
of  the*  central  United  States.  They  slope  gently  away 
from  the  mountains  of  central  Asia.  They  have  a  mod- 
erate altitude  above  sea  level  and  preserve  a  generally 
even  surface  over  hundreds  of  miles.  Marshes  and  shal- 
low lakes  lie  in  faint  depressions,  as  if  the  hollows  in  the 
original  surface  of  the  plains  had.  not  yet  been  drained  by  * 
river  action.  The  narrow  valleys  are  few  and  far  between ; 
they  can  never  be  cut  deep  while  the  region  stands  low, 
and  they  have  not  yet  been  worn  wide. 

The  more  northern  part  of  these  plains  is  treeless  because 
the  ground  is  frozen.  The  central  part  is  forested;  but 
south  of  latitude  50°  to  55°  the  plains  have  a  light  rainfall 
and  are  again  treeless;  clothed  with  thin  grass  in  summer; 
cold,  barren,  and  wind  swept  in  winter. 

The  treeless  plains  have  long  been  the  home  of  wander- 
ing tribes,  whose  wealth  is  not  in  fixed  possessions,  but  in 
herds  and  flocks  driven  from  place  to  place  for  pasture. 
The  people  live  in  tents  and  move  about  without  definite 
limits  to  their  lands.  On  account  of  their  wandering 
habits  they  are  called  nomads  (wanderers).  Every  man 
is  necessarily  a  horseman,  skilled  in  nearly  all  the  arts  of  a 
wandering  life. 


PLAINS  AND  PLATEAUS 


J 


161 


103.  Belted  Inland  Plains.  — In  Wisconsin,  far  inland 
from  the  ocean,  the  northern  part  of  the  state  is  occupied 
V  rugged  highlands  of  resistant  rocks.  Adjoining  on  the 
south  and  east  are  plains  and  uplands  arranged  in  belts, 
their  rock  layera  slopino^  pfcntly  away  from  the  highlands 
and  lapping  one 
over  another  like 
great  shingles. 

Fragments  of  the 
highland  rocks  are 
found  in  the  lower 
members  of  the  over- 
lapping strata;  nu- 
merous marine  fossils, 
like  corals  and  shell- 
fish, occur  in  many 
layers.  All  the  lay- 
ers are  well  consoli- 
dated ;  the  firmer 
ones  form  belts  of 
hilly  uplands,  between  which  the  weaker  layers  are  worn 
down  to  lower  plains. 

Although  the  sea  may  now  be  a  thousand  miles  away, 
the  belts  of  upland  and  plain  are  easily  seen  to  be  similar 
to  the  belted  coastal  plains  already  described,  while  the 
rugged  highlands  are  the  older  land  from  which  the  strata 
of  the  plains  and  uplands  were  long  ago  derived. 

This  is  an  ancient  coastal  plain ;  that  is,  a  region  that 
began  its  existence  as  a  coastal  plain  ages  ago  in  the 
earth's  history,  when  the  continent  was  small,  and  that 


Fig.  74.    Ancient  Coastal  Plain  of  Wisconsin 


162  ELEMENTARY  PHYSICAL  GEOGRAPHY 

now  stands  in  the  interior  of  the  continent  because  later 
uplifts  have  added  still  more  land. 

Belted  inland  plains,  similar  to  the  example  in  Wiscon- 
sin, occur  in  many  parts  of  the  world,  usually  presenting 
a  succession  of  hilly  uplands  and  intermediate  plains  sim- 
ilar to  those  here  described.  Good  examples  are  found 
in  south-central  England  and  in  northeastern  France. 
They  all  enjoy  the  advantage  that  comes  from  diversity  of 
form  and  products  and  from  the  resulting  variety  of  occu- 
pations that  they  support. 

104.  Plateaus.  —  When  plains  stand  at  a  considerable 
height  above  the  sea  level  they  are  called  plateaus.  No  defi- 
nite limit  of  height  can  be  given  to  separate  the  two  classes 
of  forms.  In  elevated  regions  the  lower  parts  may  be  called 
plains,  even  though  they  are  more  than  2000  or  3000  feet 
above  sea  level;  in  low  regions  the  higher  parts  may  be  called 
plateaus,  even  though  not  higher  than  1000  or  2000  feet. 

Plateaus  are  sometimes  traversed  by  deep  and  narrow 
valleys  or  canyons,  branching  in  various  directions.  The 
canyons  are  cut  down  to  a  great  depth  by  their  streams 
because  the  plateau  surface  stands  high  above  baselevel. 

Plateaus  are  generally  built  of  horizontal  rock  layers  of 
various  kinds,  whose  edges  are  well  shown  in  the  canyon 
walls.  In  Figures  75,  76,  and  77  a  deep  cut  is  imagined 
across  the  front  of  the  view,  so  as  to  show  more  clearly  the 
rock  layers  that  crop  out  in  the  canyon  walls.  The  broad 
uplands  between  the  canyons  have  a  comparatively  even 
surface  across  which  it  is  easy  to  travel,  but  the  deep 
canyons  are  almost  impassable. 


PLAINS  AND  PLATEAUS 


163 


The  walls  of  the  narrower  canyons  consist  of  a  succession 
of  cliffs  and  slopes,  often  too  steep  to  be  climbed.  The  cliffs 
are  formed  on  the  hard  resistant  layers,  which  are  strong 
enough  to  stand  with  a  steep  face ;  the  slopes  are  formed  on  the 
weak  layers,  wliich  are  more  easily  weathered  back  to  a  slant. 


The  slopes  are  covered  with  coarse 

rock  waste,  or  talus^  weathered  from 

the  cliffs  above.  The  rock  waste  weathers  and  falls  from 
each  cliff,  and  rolls,  washes,  and  creeps  down  each  slope  to 
the  top  of  the  cliff  next  below,  where  it  falls  again,  shatter- 
ing to  fragments ;  at  last  it  reaches  the  stream,  where  its 
finer  parts  are  rapidly  washed  away.  Thus  the  cliffs  and 
slopes  wear  back  or  retreat,  and  the  canyon  widens. 

As  a  canyon  widens,  a  platform  or  bench  is  formed  on 
the  top  of  the  stronger  cliffs ;  it  is  then  often  possible  to 
descend  into  the  canyon  by  climbing  down  crevices  in  the 
cliffs,  from  platform  to  platform. 


164 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Point  out  the  cliffs,  slopes,  and  platforms  of  the  canyon  walls  in 
Figures  76  and  77.  Where  are  the  highest  cliffs,  the  longest  slopes, 
the  broadest  platforms  ?  Which  layers,  shown  in  the  front  of  the 
diagram,  are  resistant  ?     Which  are  weak  ? 

The  slow  creeping  of  waste  down  the  slopes  of  the  valley 
sides  is  caused  by  very  slight  movements  of  the  fragments 
and  particles  as  they  warm  by  day  and  cool  by  night,  as 


Fig.  76.    Diagram  of  a  Narrow  Canyon 

they  are  wet  by  rain  and  dried  in  fair  weather,  or  as  they 
are  moved  by  the  freezing  and  thawing  of  films  of  water 
between  them.  The  movement  is  more  noticeable  on  steep 
slopes,  but  it  does  not  cease  even  on  the  gentler  slopes. 

The  slow  downhill  creeping  of  weathered  fragments, 
aided  by  the  surface  washing  of  fine  particles  in  wet 
weather,  is  the  chief  means  of  moving  waste  down  from 
the  high  ground  to  the  streams  in  the  valley  bottoms. 

As  the  canyon  is  eroded  by  the  main  river,  ravines  are  cut 
in  the  canyon  walls  by  streams  that  rise  on  the  plateau. 


PLAINS  AND  PLATEAUS  165 

The  deeper  the  main  canyon  is  eroded,  the  deeper  the 
side  ravines  are  worn  down,  and  the  more  the  plateau  is 
dissected.  Yet  in  the  stage  shown  in  Figure  77  the  great 
work  of  wearing  away  the  plateau  Ls  only  well  begun. 

Tlie  lofty  plateaus  of  northern  Arizona  are  traversed  from 
east  to  west  by  the  Grand  canyon  of  the  Colorado,  from 
4000  to  5000  feet  deep.     The  dry  cliinate  of  the  plateau 


Fig.  77.    Diagram  of  a  Widened  Canyon 

makes  vegetation  scanty.  The  region  offers  no  temptation 
to  settlement,  however  marvelous  it  is  to  the  explorer. 
Much  of  it  is  desolate,  occupied  by  a  few  Indians,  who 
subsist  by  "cultivating  little  patches  of  com,  gathering 
seeds,  eating  the  fruits  and  fleshy  stalks  of  cactus  plants, 
and  catching  a  rabbit  or  lizard  now  and  then;  dirty, 
squalid,  but  happy,  and  boasting  of  their  rocky  land  as 
the  very  Eden  of  the  earth." 

The  great  elevation  of  this  plateau  permits  an  unusual 
depth  of  canyon  cutting.     The  massive  strong  and  weak 


166  ELEMENTARY  PHYSICAL  GEOGRAPHY 

strata  of  which  the  plateau  is  built  produce  strong  cliffs 
and  long  talus  slopes  on  the  canyon  walls.  Far  down  in 
the  bottom  of  the  great  trench  runs  the  tawny  Colorado, 
turbid  with  waste  that  is  showered  from  the^walls  in  rocky 
avalanches  or  swept  in  from  side  canyons  by  cloud-burst 
torrents.  The  water,  bearing  abundant  waste,  is  still  rasp- 
ing down  the  rocks  in  its  falls  and  rapids.  Deep  as  the 
canyon  is,  it  has  been  cut  down  only  by  the  river.  There 
is  no  indication  of  clefts  or  fractures  along  the  river  course. 

Unlike  most  great  rivers  whose  valleys  serve  as  paths  of 
travel,  the  Colorado  is  almost  inaccessible  along  its  canyon. 
Only  one  exploring  party  has  successfully  gone  down  the 
canyon,  and  their  narrative  is  a  wonderful  history  of  scien- 
tific adventure.  When  their  boats  once  entered  the  canyon, 
retreat  was  impossible  against  the  swift  current.  Escape 
by  climbing  the  walls  was  hazardous.  To  descend  the  river 
was  easy  on  its  smooth  stretches,  even  though  hemmed  in  by 
great  chffs ;  but  cascades  plunge  over  ledges  where  the  most 
resistant  rock  layers  are  not  yet  cut  through,  and  rocky 
rapids  obstruct  the  channel  where  side  canyons  deliver 
heaps  of  bowlders  to  the  main  river.  After  many  perils 
the  party  came  out  to  the  open  lower  country  on  the  west. 

Plateaus  interrupted  by  narrow  canyons  are,  as  a  rule, 
occupied  only  on  their  upland  surface.  The  elevation  of 
the  upland  is  an  advantage  in  the  torrid  zone,  where  the 
high  temperatures  at  sea  level  are  willingly  exchanged  by 
civilized  races  for  a  more  moderate  temperature  at  altitudes 
of  several  thousand  feet.  But  in  the  temperate  zone  a 
high  plateau  is  at  a  disadvantage  from  the  rigor  of  its 
winters,  as  well  as  from  its  difficulty  of  access. 


PLAINS  AND  PLATEAUS  167 

The  canyonlike  valleys  are  obstacles  to  movement ;  they 
serve  as  barriers  (except  to  birds  and  winged  seeds)  between 
the  uplands  on  each  side.  They  are  seldom  inhabited, 
unless  by  the  people  of  a  persecuted  tribe,  who  sometimes 
take  refuge  a«  "cliff  dwellers"  in  the  recesses  or  caves 
that  are  often  excavated  between  cliff  base  and  talus  top. 

105.  Dissected  Plateaus.  —  The  rugged  uplands  that 
extend  continuously  from  New  York  to  Alabama,  known 
as  the  Catskill,  Allegheny,  and  Cumberland  plateaus,  may 
here  be  treated  together  under  the  second  name.  The 
whole  region  is  occupied  by  mountainlike  hills  and  spurs, 
built  of  nearly  horizontal  rock  layers  and  separated  by 
numberless  deep  valleys  that  have  been  eroded  by  the  riv- 
ers and  their  branching  streams.  The  hilltop  view  gen- 
erally discloses  a  rather  even  sky  line,  which  may  be  taken 
to  mark  a  plateau  surface  that  once  extended  over  the 
whole  region,  before  the  branching  valleys  were  carved. 

The  Allegheny  plateau  is  now  thoroughly  dissected  by 
its  streams.  It  is  evidently  in  a  more  advanced  stage  of 
change  than  a  plateau  that  has  only  a  few  narrow  canyons. 
The  altitude  of  the  original  upland  in  West  Virginia 
(roughly  2500  or  3500  feet)  has  been  great  enough  to  per- 
mit the  erosion  of  valleys  1000  feet  or  more  in  depth; 
hence  some  of  the  plateau  remnants  fairly  deserve  the 
popular  name  of  "  mountains,"  locally  applied  to  them. 

Many  resistant  sandstone  layers  stand  out  in  cliffs  from 
ten  to  fifty  feet  high.  As  the  layers  are  nearly  horizontal, 
the  cliffs  run  in  bands  around  the  spurs  of  the  great 
hills,  but  are  usually  hidden  by  the  heavy  forest  that 


168 


ELEMEN^TARY  PHYSICAL  GEOGRAPHY 


covers  much  of  this  region.  The  weak  strata  occupy  the 
intervening  slopes,  covered  with  a  thin  stony  soil  and  sup- 
porting forest  trees.  The  hills  and  spurs  are  all  very 
much  alike,  for  they  have  been 
dissected  by  similar  streams. 

Every  side  valley  resem-   //'^^'Z-^y  ^  /fc^w^mr  y  o  i 
bles    its    neighbors ; 
all   the  members 
of  a  local  tribe 
of    small 

streams  /  ^    Tw  v   i  '  •  i,no,„rg/  ^    .;x:"" ^cascade 

down  over 
the    same 
number  of  fall- 
making  strata  in 
their    descent    to    the 
larger  rivers. 
In  contrast  to  the  previous 
example,  this  district  has  nearly 
everywhere  lost  its  once  continuous 
upland  surface  and  is  now  transformed 
into  a  well-dissected  hill-and-valley  country, 
great  part  of  the  surface  consists  of  hillside 
slopes.     Drainage  is  not  delayed  on  extensive 
uplands ;  but  at  times  of  rain  or  winter  thaws 
water  is  quickly  shed  from  the  hills,  and  the 
main  streams  rise  rapidly  in  destructive  floods. 
The  forests  retard  but  do  not  prevent  the  wash  of  waste 
from  the  steep  slopes ;  a  great  load  of  waste  is  delivered  by 
the  side  streams  to  the  rivers. 


Fig.  78 
The  Allegheny- 
Plateau 


PLAINS  AND  PLATEAUS 


169 


What  parts  of  what  states  are  occupied  by  the  Allegheny  plateau  V 
Which  state  has  the  greatest  part  of  its  area  in  the  plateau  ?  Wliat 
cities  can  you  name  in  that  state  ?  How  far  is  it  from  the  Catskill 
mountain  district  to  the  Cumberland  plateau  district? 

As  a  whole,  the  Allegheny  plateau  is  so  rugged  that  its 
population  is  small,  being  generally  found  on  isolated  farms 


Fig.  79.    Canyon  of  Kanawha  River  in  Allegheny  Plateau,  West  Virginia 

upon  the  disconnected  uplands,  in  villages  and  occasional 
small  cities  in  the  valleys,  or  gathered  about  mines  or 
other  industrial  works.  The  isolated  hilltop  farmers  can- 
not afford  to  construct  and  maintain  good  hillside  roads ; 
it  is  difficult  to  haul  upland  products  down  bad  roads  to 
village  markets  or  to  railroad  stations,  and  it  is  doubly 
difficult  to  haul  supplies  up  to  the  farms.  Life  on  the 
uplands  is  laborious. 

The  hillsides  are  generally  too  steep  for  cultivation ;  if 
cleared,  the  soil  is  rapidly  washed  away.     Wild  animals, 


170  ELEMENTARY  PHYSICAL  GEOGRAPHY 

such  as  deer  and  bear,  almost  exterminated  from  the  lower 
country  on  the  east  and  west,  still  find  refuge  here ;  small 
game  is  abundant,  and  hunting  is  almost  as  much  of  an 
occupation  to  the  "  mountaineers  "  as  farming. 

The  forests  supply  lumber  to  the  more  thickly  settled 
communities  on  the  east  and  west.  The  numerous  coal 
seams  (vegetable  deposits  in  ancient  marshes,  now  members 
of  the  great  series  of  horizontal  strata  that  build  the 
plateau)  are  well  exposed  on  the  sides  of  the  deep-cut 
valleys,  and  are  now  extensively  mined.  Iron  ore  occurs 
in  certain  strata.  Rock  oil  and  natural  gas  are  found  by 
boring  deep  wells.  It  is  chiefly  in  connection  with  the 
industries  dependent  on  these  important  products  that  a 
larger  population  is  to-day  attracted  to  this  rough  country. 
In  the  earlier  history  of  the  United  States  the  dissected 
Allegheny  plateau  was  (excepting  the  North  Carolina 
mountains)  the  most  formidable  barrier  between  the  Atlan- 
tic coastal  plain  and  the  open  prairies  of  the  Ohio  valley. 

Intercourse  and  traffic  are  still  so  difficult  in  the  districts 
of  stronger  relief,  away  from  the  lines  of  travel,  that  the 
people  of  the  Allegheny  plateau  are  slow  in  acquiring  the 
ways  of  civilization.  Family  feuds  are  still  maintained 
among  the  "mountaineers"  of  West  Virginia  and  Ken- 
tucky. As  the  uplands  decrease  in  height  westward,  and 
the  valleys  become  more  open  toward  the  Ohio  river,  popu- 
lation increases ;  but  Pittsburg  is  a  city  of  exceptional  size 
in  this  region.  Its  growth  in  early  years  was  favored  by 
its  position  mth  reference  to  the  lower  Ohio  valley,  and  in 
later  years  by  the  great  stores  of  mineral  wealth  in  the 
surroTinding  country. 


PLAINS  AND  PLATEAUS  171 

106.  Mesas.  —  Broad  plains  of  gently  rolling  surface, 
drained  by  streams  in  wide-open,  fiat-floored  valleys,  are 
sometimes  overlooked  by  flat-topped  ** table  mountains" 
of  liorizontal  rock  layers.  Neighboring  tables  are  of  nearly 
uniform  height,  each  one  being  capped  by  the  same  kind 
of  cliff-making  rock  layers  and  flanked  by  a  sloping  talus. 
In  the  western  United  States  tables  of  moderate  height  are 
often  given  the  Spanish  name  mesa  (table;  pron.  may-8a)\ 
while  the  smaller  mesas  are  known  by  the  French  name 
hutte  (target  or  landmark ;  pron.  hewt). 

Mesas  and  buttes  of  this  kind  are  all  that  now  remain 
of  a  plateau  that  once  spread  far  and  wide  over  the  region. 
The  open  space  between  the  mesas  has  been  produced 
by  the  widening  of  the  valleys,  so  that  their  floors  now 
occupy  a  great  part  of  the  surface.  The  original  level  of 
the  plateau  may  have  been  much  higher  than  the  tops  of 
the  mesas,  for  the  uppermost  strata  may  now  be  com- 
pletely washed  away.  A  region  of  this  kind  represents  an 
approach  to  what  may  be  called  the  old  age  of  a  plateau, 
when  even  the  mesas  will  be  worn  away,  leaving  an 
unbroken  plain.  It  is  very  unlike  the  youth  of  the  plateau, 
when  the  uplands  were  broad  plains  and  the  valleys  were 
narrow  canyons. 

The  plains  of  western  New  Mexico  are  surmounted  by 
numerous  mesas  or  plateau  remnants.  Settlement  here  is 
chiefly  limited  to  the  lower  lands.  The  isolated  mesas  and 
buttes,  rising  several  hundred  feet  above  the  plains,  are 
generally  uninhabited. 

The  mesas  of  an  old  plateau  are  not,  like  the  canyons  of 
a  young  plateau,  serious  obstacles  to  travel;  for  while 


172 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


canyons  continue  for  long  distances  and  are  everywhere 
difficult  to  cross,  mesas  are  generally  of  moderate  length, 
and  many  broad  passages  are  opened  among  them.  They 
are  occasionally  occupied  as  natural  citadels  by  barbarous 
tribes. 

One  of  the  most  remarkable  remnants  of  an  old  plateau 
is  the  so-called  Enchanted  mesa  of  western  New  Mexico. 


Fig.  80.    The  Enchanted  Mesa,  New  Mexico 


It  rises  more  than  400  feet  above  the  surrounding  plain, 
and  although  no  longer  inhabited,  it  was  once  occupied  by 
a  small  tribe  of  Indians,  who  found  safety  on  its  almost 
inaccessible  summit. 

Other  mesas  in  New  Mexico  and  Arizona  are  still 
occupied  by  Indians,  whose  compact  groups  of  houses  on 
the  upland  cannot,  at  a  little  distance,  be  distinguished 
from  the  rock  walls  of  the  cliffs.  The  Indians  cultivate 
small  patches  of  corn  on  the  lower  ground,  but  they  have 
not  ventured  to  build  villages  there  for  fear  of  attack  from 
more  warlike  tribes. 


PLAINS  AND  PLATEAUS 


173 


In  the  interior  of  British  Guiana  gigantic  remnants  of  an 
old  phvteau  rise  above  the  surrounding  lower  country.  Huge 
mesas  are  rimmed  round  by  almost  inaccessible  cliffs  that 
stand  above  long  talus  slopes.  One  of  the  highest  is  Roraima, 
whose  broad  tiible  is  more  than  2000  feet  above  its  base.  It 
is  uninhabited,  and  until  recently  had  never  been  ascended. 


Fig.  81.    Broken  Plateaus 


107.  Broken  Plateaus.  —  The  plateaus  of  northern  Ari- 
zona, of  which  the  Sheavwits  already  described  is  one, 
stand  in  a  curious  relation  to  one  another.  East  of  the 
Sheavwits  comes  the  Uinkaret,  presenting  the  same  upland 
(diversified  by  volcanic  cones  and  lava  flows),  and  expos- 
ing the  same  succession  of  cliffs  and  talus  slopes  in  the 
canyon  walls;  but  the  Uinkaret  stands  about  1800  feet 
higher  than  the  Sheavwits.  The  two  are  separated  by  a 
high  and  ragged  cliff,  or  escarpment  (CA,  Figure  81), 
known  as  Hurricane  ledge,  facing  westward; 


174 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


The  section  exposed  in  the  canyon  {A,  Figure  81) 
shows  that  the  cliff  stands  on  the  line  of  a  great  north- 
and-south  fractui^e,  which  divides  the  whole  mass  of 
strata  into  two  blocks,  the  eastern  block  (Uinkaret) 
being  lifted  nearly  2000  feet  higher  than  the  western 
(Sheavwits).  Several  other  similar  plateau  blocks  are 
found  in  this  region.     The  displacement  of  the  blocks  is 


Fig.  82.    Hurricane  Ledge,  a  Dissected  Fault  Cliff 


clearly  represented  in  the  section  on  the  right  front  of  the 
diagram,  Figure  81,  under  the  letters  D,  B,  E. 

The  western  boundary  of  the  Sheavwits  plateau  {FD^ 
Figure  81)  is  one  of  these  cliffs  of  displacement,  2000  or 
3000  feet  high.  It  is  cut  by  gigantic  ravines,  from  which 
great  volumes  of  rock  waste  are  washed  out. 

Fractures  of  this  kind,  on  which  adjacent  blocks  of  land 
are  displaced,  are  called  faults.  The  cliffs  that  originate 
on  the  broken  face  of  the  uplifted  blocks  are  called  fault 
cliffs.     They  are   in   time   more  or  less  worn   back   by 


PLAINS  AND  PLATEAUS  175 

weathering  and  by  the  growth  of  ravines,  such  being  the 
present  stage  of  Hurricane  ledge;  and  they  may  then 
be  called  dissected  fault  cliffs. 

The  forces  by  which  the  plateau  blocks  have  been 
broken  and  lifted  have  not  been  fully  explained.  It  is 
probable  that  violent  earthquakes  accompanied  the  produc- 
tion of  the  fractures,  and  that  the  displacement  of  the 
blocks  was  accomplished  by  many  small  movements,  each 
causing  a  moderate  earthquake. 

QUESTIONS 

Sec.  96.  Describe  the  natural  processes  in  operation  on  a  moun- 
tainous district  bordering  the  sea.  Consider  the  relation  of  such  a 
district  to  habitation.     Give  an  example. 

97.  Describe  a  narrow  coastal  plain.  Describe  its  valleys  and 
their  lateral  ravines.  Explain  their  origin.  What  can  be  inferred 
as  to  the  future  form  of  such  a  plain  ?  as  to  its  past  form  ?  How 
can  the  origin  of  such  a  plain  be  accounted  for?  Define  baselevel, 
and  state  the  relation  of  rivers  and  valleys  to  baselevel.  Describe 
a  narrow  coastal  plain  in  Scotland ;  in  Oregon ;  in  Mexico. 

98.  Describe  a  broad  coastal  plain.  What  is  meant  by  relief? 
Describe  the  coastal  plain  of  the  South  Atlantic  States  as  to  form ; 
as  to  soil ;  as  to  industries.  Why  are  its  soils  arranged  in  belts  ? 
Compare  it  with  the  narrow  coastal  plain  of  Scotland.  What 
products  are  derived  from  it? 

99.  Describe  a  belted  coastal  plain.  What  is  the  origin  of  its 
form  ?  What  is  a  cuesta  ?  Describe  the  course  of  the  streams  with 
respect  to  a  cuesta.    Describe  the  belted  coastal  plain  of  New  Jersey. 

100.  Describe  an  embayed  coastal  plain  as  to  hills,  valleys,  and 
bays.  Explain  its  origin.  How  has  the  depression  of  the  region 
affected  the  form  of  the  coast  line?  Describe  an  example  of  this 
class.  Describe  its  effects  on  the  distribution  and  occupation  of  its 
population ;  on  the  location  of  roads,  villages,  and  cities. 


176  ELEMENTARY  PHYSICAL  GEOGRAPHY 

101.  Where  may  falls  be  expected  in  rivers  that  cross  coastal 
plains?  What  is  the  cause  of  the  falls?  .  What  is  the  fall  line? 
Where  are  cities  likely  to  be  situated  on  the  rivers  of  coastal  plains  ? 
What  cities  lie  on  the  fall  line  of  the  Atlantic  coastal  plain? 

102.  Describe  the  Great  plains  of  the  central  United  States  as  to 
origin,  form,  climate,  vegetation,  and  industries.  Describe  the 
extension  of  these  plains  into  Canada  as  to  climate  and  vegetation. 
Describe  the  plains  of  western  Siberia  as  to  form,  climate,  and  popu- 
lation. Why  are  the  valleys  in  these  plains  shallow?  What  is 
the  relation  between  nomads  and  inland  plains? 

103.  What  is  a  belted  inland  plain  ?  Describe  an  example  from 
Wisconsin.  Explain  its  origin.  Where  may  some  other  inland 
belted  plains  be  found? 

104.  Compare  plains  and  plateaus.  Describe  a  canyon  as  to 
form  and  origin.  Compare  the  form  of  the  canyon  walls,  as  shown 
in  the  diagrams  of  a  narrow  and  a  widened  canyon.  Explain  their 
differences.  What  is  the  relation  of  strong  and  weak  rock  layers  to 
form  ?  Describe  the  movement  of  rock  waste  in  a  canyon.  Describe 
the  plateaus  of  northern  Arizona.  Describe  the  Colorado  river  and 
its  canyon.  Why  is  it  difl&cult  to  follow  the  river?  What  is  the 
value  of  plateaus  to  habitation?  of  canyons  as  barriers? 

105.  What  is  a  dissected  plateau?  Describe  the  Allegheny  plateau 
as  to  location,  extent,  altitude,  and  form.  Describe  the  hillsides; 
the  streams ;  the  drainage ;  the  industries ;  the  products  of  this 
plateau.     What  is  the  condition  of  its  people? 

106.  Describe  mesas  and  their  surroundings.  How  are  mesas 
formed?  Compare  a  mesa  and  a  canyon.  Compare  the  plateaus  of 
northern  Arizona,  the  dissected  Allegheny  plateau,  and  the  mesa 
district  of  New  Mexico.     Describe  the  Enchanted  mesa ;  Roraima. 

107.  What  is  meant  by  broken  plateaus?  Describe  the  broken 
plateaus  of  northern  Arizona.  How  are  they  separated?  What  is  a 
fault?  a  fault  cliff?  a  dissected  fault  cliff?  What  is  the  relation  of 
earthquakes  to  broken  plateaus? 


CHAPTER  VI 
MOUNTAINS 

108.  Mountain  Ranges. — The  peaks  and  ridges  of  moun- 
tains are  generally  grouped  in  belts  of  much  greater  length 
than  breadth,  called  mountain  ranges.  When  several  ranges 
are  grouped  together  they  constitute  a  mountain  chain. 
Unlike  plains  and  plateaus,  in  which,  as  has  been  stated  in 
the  preceding  chapter,  the  rock  layers  are  nearly  horizontal, 
mountain  ranges  are  belts  of  disordered  structure  in  the 
earth's  crust.  Sometimes  the  strata  are  broken,  displaced, 
and  tilted  as  if  gradually  disturbed  by  some  great  uplifting 
force  from  beneath;  sometimes  the  strata  are  bent  and 
folded,  as  if  slowly  compressed  by  some  irresistible  crush- 
ing force  from  one  side. 

The  origin  of  the  forces  which  produce  mountains  is 
not  fully  understood.  One  of  the  most  ingenious  and 
satisfactory  theories  accounts  for  many  ranges  as  great 
disorderly  folds  formed  in  the  crust  of  the  earth,  which 
is  thought  to  wrinkle  here  and  there  as  it  very  grad- 
ually settles  down  on  the  slowly  cooling  and  contracting 
interior. 

Streams  carve  deep  valleys  in  the  uneven  surface  pro- 
duced by  mountain  upheaval.  Mountains  as  we  see  them 
are  therefore  the  result  of  deforming  forces  which  slowly 

177 


178 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


raise  the  mountain  belt  to  great  height,  and  of  eroding 
forces  which  still  more  slowly  wear  down  the  uplifted  belt 
by  carving  valleys  in  it. 


Fig.  83.    A  Mountain  Peak 


109.  Block  Mountains.  —  In  southern  Oregon  and  the 
adjoining  parts  of  California  and  Nevada  there  are  many 
long  narrow  mountain  ridges,  extending  about  north  and 
south.     Each  ridge  is  a  few  miles  wide,  ten  to  forty  miles 


MOUNTAINS  179 

long,  and  1000  or  more  feet  high.  The  ridges  are  steep 
or  cliff-like  on  one  side,  of  gentler  slope  on  the  other,  and 
are  separated  by  flat  trough-like  depressions  of  varying 
breadth  and  depth.  A  general  view  of  the  country  shows 
that  the  entii*e  region  was  once  a  plain,  but  that  it  has  been 
gradually  broken  into  long  narrow  blocks,  and  that  the 
blocks  are  tilted  one  way  and  the  other,  so  that  their 
uplifted  edges  form  the  mountain  crests. 


Fig.  84.    Block  Mountains 

Which,  block  mountain  is  completely  shown  in  Figure  84  ?  How 
does  it  end  ?  (Note :  the  space  included  in  the  figure  is  too  small 
to  show  the  whole  length  of  most  of  the  mountains  ;  the  northern 
part  of  some  and  the  southern  part  of  others  are  cut  off.)  Describe 
a  large  block  mountain ;  its  crest  line,  its  cliff  face,  its  back  slope. 
Where  could  it  be  best  ascended  ? 

Some  of  the  ridges  still  preserve  the  form  of  the  tilted 
blocks,  hardly  changed  by  weathering ;  their  sloping  backs 
are  smooth;  their  cliff ed  fronts  have  little  talus  at  the 
base.  Others  have  shallow  gullies  worn  down  the  back, 
while  the  cliffs  are  indented  by  ravines,  and  every  ravine 
has  a  fanlike  deposit  of  rock  waste  spread  out  beneath  it ; 


180 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


between  the  fans  the  cliffs  have  a  distinct  talus  slope  at 
their  base.  Yet  the  mountain  blocks  of  Oregon  are,  on 
the  whole,  so  little  worn  that  they  must  have  been  broken 
and  tilted  recently  in  the  earth's  history. 

Earthquakes  are  not  infrequent  in  this  region ;  hence  it 
is  believed  that  the  tilting  of  the  blocks  is  still  in  progress 
from  time  to  time  ;  a  movement  of  even  a  few  inches  would 
suffice  to  cause  earth  tremors,  while  a  sudden  start  of  a  foot 

or  more  would  produce 
a  violent  and* destructive 
shock  for  many  miles 
around,  gradually  fad- 
ing away  at  greater  dis- 
tances. There  is  no  sign 
that  volcanic  action  has 
any  connection  with  the 
fractures  and  earth- 
quakes of  this  region. 
The  drainage  of  the 
block  mountains  is  very 
simple,  for  the  streams  follow  the  slopes  produced  by  the 
tilting  of  the  blocks.  The  smaller  wet-weather  streams  flow 
down  the  slopes  of  the  ridges.  Larger  streams  flow  along 
the  troughs  in  the  direction  of  their  slant  to  the  deepest 
depressions,  and  there  form  shallow  lakes  and  marshes. 
The  finer  waste  from  the  ridges  is  spread  evenly  over  the 
lower  parts  of  the  troughs,  concealing  their  rocky  floor. 

Certain  features  of  the  region  depend  on  its  arid  climate. 
The  rainfall  is  light  (fifteen  inches  or  less  a  year),  for  the 
Sierra  Nevada  and  Cascade  ranges  on  the  west  take  most 


Fig  85.    Mountains  of  Southern  Oregon 


MOUNTAINS  181 

of  the  moisture  from  the  Pacific  winds.  Few  of  the  lakes 
are  filled  to  overflowing ;  they  discharge  their  water  supply 
by  evaporation  into  the  dry  air.  Most  of  the  lakes  are 
therefore  saline,  and  the  plains  of  fine  waste  about  them 
are  barren. 

In  dry  seasons  the  lakes  shrink ;  some  of  them  disappear, 
leaving  smooth  floors  of  sun-baked  clay.  The  bottom  of  the 
troughs  elsewhere  and  the  lower  slopes  of  the  ridges  are 
clothed  with  bunch  grass  and  sagebrush ;  the  ridge  slopes, 
receiving  more  rainfall  than  the  lower  lands,  support 
scattered  cedars,  and  the  higher  crests  bear  forests  of  pine 
and  spruce. 

Although  the  ridges  are  of  moderate  height,  they  repel 
the  few  settlers  in  the  region,  whose  ranches  are  all  found 
in  the  troughs.  The  thin  grass  supports  scattered  herds 
of  cattle,  and  the  streams  suffice  for  a  little  irrigation. 
Thus  even  in  these  low  young  ridges  the  effect  of  moun- 
tains on  climate,  distribution  of  vegetation,  and  location 
of  settlements  is  well  shown. 

110.  Dissected  Ranges.  —  In  Nevada  and  the  adjoining 
parts  of  California  and  Utah  there  are  many  north-and- 
south  mountain  ranges  from  twenty  to  eighty  miles  long, 
and  from  five  to  twenty  miles  wide.  Their  summits  rise 
from  5000  to  7000  feet  above  the  plains.  Their  crests 
are  notched  and  uneven ;  their  slopes  are  varied  by  well- 
carved  spurs  between  deep  valleys.  The  troughs  between 
the  ranges  contain  long  slopes  of  gravelly  waste  that  have 
spread  out  from  the  valleys  when  the  streams  are  flooded. 
As  compared  with  the  ridges  of  southern  Oregon,  these 


182  ELEMENTARY  PHYSICAL  GEOGRAPHY 

ranges  are  larger  and  more  dissected.  They  possess  more 
of  the  beauty  and  variety  of  form  generally  found  in 
mountains. 

The  ranges  of  Nevada,  like  the  ridges  of  Oregon,  seem 
to  have  been  formed  by  the  uplifting  of  long  blocks  of  the 
earth's  crust;  but  in  Nevada  the  blocks  must  have  been 


Fig.  86.    A  Dissected  Mountain  Range,  Utah 

larger  and  the  uplifting  greater;  and  the  uplifting  must 
have  begun  earlier  than  in  Oregon,  for  the  work  of  dis- 
section by  streams  is  here  much  further  advanced.  The 
ranges  of  Nevada  are  thoroughly  or  maturely  dissected. 
Yet,  as  in  Oregon,  occasional  earthquakes  show  that  the 
mountains  are  still  growing. 

The  higher  ranges  in  Nevada  exhibit  more  distinctly 
than  the  smaller  ranges  of  Oregon  the  lower  temperature, 


MOUNTAINS  188 

with  greater  cloudiness  and  rainfall,  that  prevails  on  the 
mountains  as  compared  with  the  plains  between  them. 
The  rainfall  on  the  plains  is  light,  but  storm  clouds 
often  gather  round  the  peaks  while  the  sun  shines  else- 
where. When  the  clouds  dissolve,  the  mountains  have 
been  refreshed  by  rain  or  whitened  with  snow,  while  the 
plains  may  be  as  dry  as  before,  except  where  the  turbid 
flooded  streams  rush  out  from  the  mountain  valleys.  The 
streams  generally  wither  away  on  the  gravelly  plains. 
Settlements  in  Nevada  are  therefore  commonly  limited  to 
a  belt  around  the  mountain  base,  where  the  streams  niay 
irrigate  fields.  Some  of  the  ranges  contain  valuable  ores ; 
hence  mining  towns  have  sprung  up  in  their  valleys. 

111.  Folded  Mountains.  —  The  Jura  mountains,  along 
the  border  of  France  and  Switzerland,  occupy  a  belt  of 
country  where  the  rock  layers,  once  horizontal,  have  been 
slowly  pressed  into  a  series  of  wavelike  folds.  The  moun- 
tains consist  of  a  number  of  parallel  ranges  and  valleys 
trending  about  northeast  and  southwest.  Each  range  con- 
sists of  a  series  of  rock  layers  bent  upward  like  an  arch ; 
each  valley  is  underlaid  by  the  same  series  of  layers  bent 
downward  like  a  trough.  Some  of  the  uppermost  layers 
have  been  weathered  off  from  the  crest  of  the  arches; 
the  edges  of  the  harder  layers  remain  in  flanking- ridges. 
Waste  from  the  arches  has  accumulated  in  the  troughs, 
flooring  them  with  gravel  and  sand. 

The  rock  layers  of  these  mountains  contain  sea  fossils ; 
the  layers  must  originally  have  been  horizontal  strata  on 
the  floor  of  an  ancient  sea.     Since  then  they  have  gradually 


184 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


been  pressed  and  folded  into  their  arch-and-trough  struc- 
ture by  a  powerful  side  pressure. 

The  drainage  of  the  Jura  mountains  is,  for  the  most  part, 
like  that  of  the  Oregon  ridges  in  following  the  slopes  of 
the  deformed  surface.  Short  streams  run  down  the  sides 
of  the  arches,  cutting  ravines  on  the  slopes,  as  shown  in 


Fig.  87.    Diagram  of  the  Jura,  a  Folded  Mountain  Range 

the  unshaded  foreground  of  Figure  87.  Larger  streams 
gather  on  the  trough  floors  and  escape  at  one  end  or  the 
other  as  opportunity  offers.  Here  and  there  a  stream  cuts 
across  an  arch,  wearing  a  deep  gorge  from  one  trough 
valley  to  the  next,  and  exhibiting  the  arched  structure,  as 
in  the  middle  ridge  of  Figure  87. 

Where  are  the  Jura  mountains  ?  How  many  arches  are  shown  in 
Figure  87  ?  How  many  troughs  ?  What  is  their  trend  ?  How  many 
cross  valleys?     If  you  were  traveling  there,  where  would  you  go  to 


.  MOUNTAINS  185 

see  the  arched  rock  layers  ?  Where  does  the  topmost  layer  lap  over 
an  arch?  What  forms  result  where  the  topmost  layer  has  been 
partly  worn  away  ?  Describe  the  course  of  some  of  the  small  streams 
that  rise  on  the  top  of  an  arch. 

As  ill  all  mountains  of  distinct  relief,  the  form  of  this 
range  exercises  a  strong  control  over  the  distribution, 
occupation,  and  movement  of  the  population.  The  valley 
floors  are  well  settled;  villages  often  lie  near  the  mouths 
of  transverse  gorges.  Roads  are  generally  limited  to  the 
lengthwise  and  crosswise  valleys.  Byways  and  footpaths 
lead  to  the  upland  fields  and  pastures.  Little  villages  are 
sometimes  found  on  the  tops  of  the  broader  arches.  The 
steeper  slopes  are  generally  forested. 

.  112.  Lofty  Mountains. — Lofty  mountain  ranges,  like  cer- 
tain parts  of  the  llocky  mountains,  but  better  represented  by 
the  Alps,  the  Caucasus,  and  the  Himalayas,exhibit  a  remark- 
able variety  of  peaks,  ridges,  ravines,  and  valleys.  Their 
higher  central  peaks  usually  consist  of  the  most  resistant 
rocks,  surrounded  by  slanting  layers  that  rise  in  great  ridges. 

These  majestic  forms  usually  depend  as  much  on  the 
deep  erosion  of  great  valleys  by  streams  as  on  their  lofty 
uplift.  .  Unlike  the  simple  tilted  blocks  of  Oregon,  or  the 
orderly  folds  of  the  Jura,  the  greater  ranges  show  little  or 
nothing  of  their  original  form. 

The  discovery  of  marine  fossils  in  the  bedded  rocks  of 
high  Alpine  ridges  toward  the  close  of  the  eighteenth  cen- 
tury was  received  with  great  astonishment  by  the  scien- 
tific men  of  the  time.  The  occurrence  of  fossils  in*  so 
elevated  a  position  was  one  of  the  first  generally  accepted 
proofs  of  the  changes  that  have  gone  on  in  the  past,  by 


186 


ELEMENTAKY  PHYSICAL  GEOGRAPHY 


which  the  present  form  of  the  earth's  surface  has  been 
fashioned.  But  not  until  the  nineteenth  century  had  well 
advanced  was  it  generally  understood  how  much  more  the 
form  of  lofty  mountains  depends  on  processes  of  land 
sculpture  than  on  forces  of  uplift. 

113.    Peaks  and  Ridges.  —  The  height  of  lofty  mountain 
summits  is  due  in  great  part  to  the  uplift  that  the  whole 


Fig.  88.    Peaks  of  the  Central  Alps 

range  has  suffered,  but  in  part  also  to  the  success  of  the 
stronger  rocks  in  resisting  the  attack  of  the  weather,  under 
which  the  weaker  rocks  have  greatly  wasted  away.  The 
waste  that  is  shed  from  the  peaks  and  ridges  creeps  and 
washes  down  into  the  valleys,  usually  leaving  the  loftiest 
summits  bare  and  sharp.  Deep  valleys  are  eroded  by  the 
streams  between  the  ridges,  and  steep  ravines  are  worn  in 
the  slopes  and  spurs.  Thus  mountain  forms  are  chiefly 
due  to  weathering  and  stream  carving. 


MOUNTAINS 


187 


The  bare  rocky  peaks  and  ridges,  rising  into  the  cold 
upper  atmosphere,  far  above  the  limits  of  vegetation,  are 
silent  deserts.  The  stillness  is  broken  only  by  the  rush 
of  storm  winds  and  the  roar  of  rock  falls  and  snowslides. 
Not  less  barren  are  the  snow  fields  and  the  talus  slopes 
on  the  higher  mountain  flanks,  and  the  slanting  reservoii-s 
of  ice  and  snow  in  the  upper  valley  heads,  from  which 


Fig.  89.    An  Alpine  Peak  of  Slanting  Layers 

slow-moving  ice  streams,  or  glaciers,  creep  down  to  the 
lower  valleys.     The  lower  slopes  are  generally  forested. 

Many  summits  in  the  Alps  are  so  sharp  that  they  are 
called  needles  or  horns.  They  rise  as  almost  inaccessible 
peaks  between  the  growing  valley  heads.  Mt.  Blanc,  the 
highest  mountain  of  the  range  (nearly  16,000  feet),  is  of 
domelike  form  with  a  heavy  snowcap;  it  is  not  yet  suf- 
ficiently dissected  by  valleys  to  take  the  form  of  sharp 
ridges  and  peaks. 


188     ELEMENTARY  PHYSICAL  GEOGRAPHY 

The  Selkirk  range  of  the  Rocky  mountains  in  Canada 
has  steep  and  bare  summits  surmounting  the  long  lower 
slopes.  The  slopes  are  covered  with  waste  that  is  slowly 
creeping  and  washing  into  the  valleys,  to  be  borne  away 
by  the  streams.  Having  an  abundant  snowfall,  the  range 
bears  extensive  snow  fields  and  glaciers.  In  the  Rocky 
mountains  of  Colorado  snow  is  less  plentiful,  snow  fields 
are  small,  and  glaciers  are  wanting.  Long  slopes  of  creep- 
ing waste  cover  the  mountain  flanks  far  up  toward  the 
summits,  as  in  Plate  I ;  craggy  peaks  of  sharp  form  are 
less  common  than  in  the  Selkirks  or  the  Alps. 

114.  Climate  of  Mountains.  —  On  extensive  plains  the 
climate — especially  the  temperature  and  rainfall — shows 
little  variation  from  place  to  place,  being  nearly  uniform 
for  hundreds  of  miles  together.  On  the  average,  one  must 
travel  from  thirty  to  sixty  miles  poleward  to  find  a  differ- 
ence of  1°  in  mean  annual  temperature.  The  same  differ- 
ence is  found  on  mountains  by  an  ascent  of  only  300  feet. 
Many  mountains  rise  so  high  that  they  receive  snow 
while  rain  falls  on  the  surrounding  lower  lands.  Lofty 
mountains  are  therefore  usually  clothed  with  snow  on  their 
higher  slopes. 

Broad  plains  may  have  only  a  scanty  rainfall  over  hun- 
dreds of  miles  together.  On  mountains  the  rainfall  rapidly 
increases  with  elevation,  although  less  may  fall  on  very 
lofty  summits  than  at  heights  of  from  5000  to  10,000  feet. 
Not  only  because  they  are  high,  but  also  because  they 
receive  much  rain  and  snow,  high  mountains  are  usually 
the  sources  of  large  rivers. 


MOUNTAINS  189 

The  small  changes  of  form  and  climate  over  broad  plains 
make  the  conditions  of  life  nearly  the  same  over  great 
areas.  A  great  diversity  of  form  and  climate  is  found  in 
mountains  within  small  distances,  and  strong  contrasts  are 
crowded  close  together. 

115.  Mountains  as  Barriers.  —  High  mountains  serve  as 
barriers  separating  the  climates  and  the  populations  of  their 
opposite  sides.  The  windward  (eastern)  slope  of  the  equa- 
torial Andes  has  a  moist  climate  because  the  damp  winds 
from  the  Atlantic,  ascending  and  cooling,  give  forth  a  heavy 
ramfall  there ;  the  western  slope  has  a  dry  climate  because 
the  same  winds,  descending  and  warming  by  compression, 
not  only  give  forth  no  more  rain,  but  eagerly  take  up  what- 
ever moisture  they  find  on  the  way.  The  eastern  slope  is 
densely  forested ;  the  western  slope  is  for  the  greater  part 
a  desert,  except  in  valley  floors  watered  by  streams. 

Moist  winds  from  the  Pacific  give  a  plentiful  rainfall 
on  the  windward  (westward)  slopes  of  the  Sierra  Nevada 
and  the  Rocky  mountains  of  the  United  States.  The  same 
winds,  descending  on  the  eastern  or  leeward  slopes,  become 
in  winter  unseasonably  warm  and  dry,  evaporating  the  light 
snow  of  the  plains  and  la5dng  bare  the  dry  tufts  of  grass, 
greatly  to  the  advantage  of  the  cattle  feeding  there.  The 
dry  wind  is  called  the  chinook.  A  similar  wind  occurs 
in  the  northern  valleys  of  Switzerland,  where  it  is  called 
the  foehn. 

The  great  populations  of  India  and  China,  representing 
different  races,  are  separated  by  the  Himalayas  and  other 
ranges  in  southern  Asia.     The  two  peoples  are  thus  so 


790  ELEMENTARY  PHYSICAL  GEOGRAPHY 

well  held  apart  that  neither  of  them  has  had  any  important 
influence  on  the  other.  Lofty  mountain  ranges  thus  rank 
with  the  oceans  in  separating  the  inhabitants  of  the  lands. 

When  low  countries  on  opposite  sides  of  a  high  range 
are  occupied  by  different  peoples  the  mountains  commonly 
serve  as  a  natural  boundary  between  them.  The  moun- 
tain range  as  a  whole  may  serve  as  a  rough  boundary 
between  uncivilized  nations ;  but  between  civilized  nations 
the  crest  line  dividing  the  rivers  of  the  opposite  slopes  is 
often  accepted  as  a  more  precise  boundary,  as  in  the 
Pyrenees  between  France  and  Spain,  where  the  river 
divide  is  generally  adopted  as  the  national  divide. 

When  the  river  divide  departs  from  the  main  range 
that  it  was  supposed  to  follow  before  the  mountains  were 
explored,  the  boundary  question  may  give  rise  to  dispute, 
as  recently  between  Argentina  and  Chile,  where  a  number 
of  Pacific  rivers  rise  on  the  pampas  of  Patagonia  and  cut 
through  the  Andes  in  deep  gorges. 

The  difficulty  of  crossing  lofty  ranges  gives  great  impor- 
tance to  the  notches,  or  passes,  in  their  central  ridges, 
through  which  travel  and  traffic  may  go  with  less  effort 
than  over  their  peaks.  The  heavy  snows  of  the  winter 
may  close  the  passes  for  several  months.  In  earlier  cen- 
turies, when  the  passes  were  traversed  only  by  paths, 
houses  of  refuge  were  often  maintained  on  the  summit  by 
monks,  as  on  the  famous  pass  of  St.  Bernard  in  the  Alps. 

It  is  mostly  within  the  last  hundred  years  that  well- 
planned  roads  have  been  constructed  over  the  chief  passes 
of  various  mountain  ranges.  The  roads  enter  the  moun- 
tains along  the  larger  valleys   and  then   zigzag  up   the 


Plate  VII.     A  Railroad  rounding  a  Spur  of  Mt.  Ouray,  Colorado 


MOUNTAINS  191 

steeper  slopes.  They  are  carefully  laid  out  so  as  not  to 
exceed  a  certain  moderate  grade, — about  five  feet  in  a  hun- 
dred. Certain  passes  are  now  crossed  even  by  railroads, 
the  ascent  from  the  valleys  being  most  ingeniously  made 
by  curves  and  "loops."  Sometimes  the  last  part  of  the 
ascent  is  avoided  by  tunneling  the  ridge  under  the  pass, 
it  being  cheaper  in  the  long  run  for  a  railroad  to  bore 
through  than  to  climb  higher. 

When  gold  had  been  discovered  in  California  and  a  new 
population  was  making  its  way  there  in  1849  and  1850, 
the  mountain  ranges  in  the  western  United  States  were  so 
formidable  a  barrier  to  travel  that  many  of  the  emigrants 
preferred  the  long  voyage  by  sailing  vessel  around  Cape 
Horn.  Those  who  went  overland  suffered  great  hardships 
in  crossing  the  mountains  by  rough  trails,  and  many  died 
on  the  way.  Since  then  the  mountains  have  been  care- 
fully explored,  the  lowest  passes  have  been  found,  and  sev- 
eral railroad  lines  now  connect  the  Central  States  with 
the  Pacific  coast. 

Mountains  are  often  climbed  for  the  exhilaration  that 
comes  from  ascending  them,  and  for  the  glorious  view  over 
the  peaks  and- valleys  that  is  gained  from  the  summits. 
Clubs  of  mountain  climbers  have  been  formed  in  many 
countries.  They  publish  narratives  of  excursions  in 
mountainous  regions.  The  ascent  of  very  lofty  moun- 
tains, above  16,000  feet  in  height,  is  made  difficult  by  the 
thinness  of  the  air  so  far  above  sea  level.  Fatal  acci- 
dents sometimes'  occur,  especially  when  inexperienced 
climbers  try  to  make  ascents  of  difficult  peaks  without 
well-trained  guides. 


192 


ELEMENTARY  PHYSIOAL  GEOGRAPHY 


116.  Avalanches.  —  The  heavy  snowfall  of  winter  often 
overloads  the  snow  banks  on  th^  higher  slopes,  and  great 
masses  of  snow  slide  down  to  lower  levels.  Summer  melt- 
ing and  rainfall  also  cause  slides,  or  avalanches  (a-val^  to  the 
valley).  Sometimes  the  snow  mass  glides  along  the  sloping 
surface  at  a  moderate  speed.    Sometimes  it  leaps  from  cliffs 


FiQ.  90.    Path  of  an  Ice  Fall  in  the  Alps 


and  falls  with  a  terrible  velocity  to  the  valleys  below;  a 
violent  blast  of  air  bursts  outward  from  beneath,  overturn- 
ing trees  hundreds  of  feet  beyond  the  reach  of  the  snow. 

Certain  villages  in  Alpine  valleys  carefully  preserve  a 
patch  of  forest  on  the  slope  above  them  as  a  protection 
from  avalanches.  Roads  and  railways  on  steep  mountain 
slopes  must  here  and  there  be  covered  in  by  long  snow- 
sheds,  over  which  the  snow  may  slide  without  blocking  or 
injuring  the  road. 

Heavy  masses  of  ice  are  occasionally  detached  from 
glaciers   that  end  on  steep    slopes,  forming  "ice  falls." 


MOUNTAINS  193 

These  are  even  more  destructive  than  avalanches  of  snow. 
An  ice  fall  over  5,000,000  cubic  yards  in  volume  broke 
from  a  glacier  on  the  slope  of  a  peak  in  the  Alps  in  Sep- 
tember, 1895  (Figure  90;  see  Figure  89,  from  a  photo- 
graph taken  before  the  fall).  It  slid  down  a  steep  slope 
two  and  a  half  miles  long,  gathered  about  1,300,000 
cubic  yards  of  rock  waste  on  the  way,  and  then  rushed 
across  the  valley  floor,  dashing  far  up  the  opposite  slope 
and  falling  back  again,  like  a  wave  from  a  cliff.  A  bench 
on  the  path  of  the  sliding  mass  caused  it  to  leap  forward, 
clear  of  the  ground;  then,  as  it  fell,  the  air  beneath  was 
violently  driven  away,  blowing  out  fragments  of  ice  and 
rock  and  breaking  down  trees  hundreds  of  yards  distant 
(shown  by  arrows  turned  to  the  right,  Figure  90). 

117.  Landslides  on  Mountain  Sides.  —  In  deep  and  nar- 
row valleys  among  mountains  the  side  slopes  are  sometimes 
cut  so  steep  that  great  rock  masses  may  be  loosened  from 
the  walls  and  slip  to  the  bottom,  forming  landslides. 

A  landslide  in  the  Alps  in  1898  destroyed  a  few  of 
the  houses  on  the  edge  of  the  village  of  Airolo,  near  the 
southern  entrance  to  the  great  St.  Gotthard  tunnel.  The 
scar  left  by  the  falling  mass  is  still  distinctly  visible  high 
up  on  the  mountain  side ;  the  fallen  rock,  greatly  shattered, 
spreads  forward  toward  the  stream  in  the  valley  floor. 
Had  the  slide  taken  a  course  a  quarter  of  a  mile  farther 
south,  it  would  have  destroyed  much  of  the  village. 

In  September,  1893,  a  great  landslide  occurred  in  the 
deep  valley  of  one  of  the  upper  branches  of  the  Ganges  in 
the  Himalayas.     In  three  days  800,000,000  tons  of  rock 


194 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


fell  with  deafening  noise,  darkening  the  air  with  dust,  leav- 
ing a  great  bare  cavity  with  steep  walls  several  thousand 
feet  high  to  mark  its  source,  and  building  a  dam  nearly  1000 
feet  deep  across  the  narrow  valley  floor.  A  lake  gradu- 
ally formed  on  the 
upstream  side  of 
the  dam  and  grew 
to  be  four  miles 
long  before  it  over- 
flowed, about  a  year 
after  the  slide. 

In  the  meantime 
the  danger  that  the 
lake  might  burst 
out  in  a  great  flood 
being  perceived  by 
the  British  engi- 
neers in  charge  of 
the  public  works  of 
India,  the  bridges 
in  the  lower  valley 
were  removed; 
safety  marks  were 
set  up  on  the  valley 
sides,  100  or  200  feet  above  the  ordinary  river  level,  indi- 
cating the  height  above  which  the  flood  would  probably  not 
rise  ;  and  a  telegraph  line  was  constructed  down  the  valley 
from  the  dam,  to  give  prompt  warning  of  the  outburst. 

The  flood  occurred  at  midnight,  August  26-27,  1894. 
In  four  hours   about  400,000,000   cubic  yards  of  water 


^' 


Fig.  91.    The  Landslide  of  Airolo,  Switzerland 


MOUNTAINS 


195 


were  discharged,  cutting  down  the  dam  nearly  400  feet, 
flooding  the  valley  to  a  depth  of  from  100  to  170  feet, 
and  rushing  forward  with  a  velocity  of  20  miles  an  hour. 
Many  miles  of  valley  road  were  washed  away.     Every 


Fio.  92.    A  Landslide  in  ttie  Himalayas 


vestige  of  habitation  was  destroyed  in  villages  along  the 
upper  Ganges ;  but  so  well  was  the  notice  of  danger  given 
that  only  one  man  lost  his  life,  and  that  because  he 
would  not  heed  the  warning.  Under  a  less  intelligent 
control,  thousands  of  people  must  have  perished  in  such  a 
catastrophe.  The  remains  of  many  other  landslides  are 
found  in  the  valleys  of  the  Himalayas. 


196 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


118.  Valleys  among  Mountains.  —  One  of  the  strongest 
characteristics  of  thoroughly  dissected,  lofty  mountains  is 
the  activity  with  which  the  rock  waste  is  weathered  from 
the  peaks  and  cliffs,  moved  down  the  precipitous  slopes. 


Fig.  93.    The  Himalaya  Mountains 


swept  by  flooded  torrents  down  steep  ravines,  and  washed 
by  streams  along  the  larger  valleys  and  out  upon  the 
adjoining  lowlands.  The  waste  seems  everywhere  to  be 
streaming  (as  the  long-lived  mountains  might  say)  down 


.  MOUNTAINS  197 

from  the  peaks  and  ridges.  The  carving  of  valleys  in  the 
mountains  has  been  accomplished  by  the  long  duration  of 
these  active  processes  for  ages  past. 

The  rock  waste -consists  of  angular  fragments  as  it  falls 
from  the  cliffs  and  ci-eeps.  down  tiie  slopes.  The  angles  are 
worn  off  as  the  waste  is  rolled  along  in  rapid  torrents, 
and  after  traveling  thus  for  a  few  miles  the  fragments  are 
well  rounded,  becoming  smaller  and  smaller  the  farther 
they  are  swept  along  the  stream  bed.  The  fine  grains 
that  are  worn  off  from  the  angles  of  the  larger  fragments 
are  borne  along  more  quickly  than  the  larger  pebbles  and 
cobbles. 

A  torrent  that  receives  much  coarse  waste  from  a  steep- 
sided  ravine  frequently  sweeps  so  much  of  it  into  the  main 
valley  that  it  cannot  all  be  carried  away  by  the  master 
river.  The  coarser  part  of  the  waste  then  accumulates  in 
a  conelike  form,  known  as  an  alluvial  fan^  spreading  with 
even  slope  from  the  ravine  mouth  into  the  main  valley. 

Alluvial  fans  have  a  steep  slope  when  formed  by  small 
torrents  bearing  a  coarse  and  plentiful  load.  They  have 
a  flat  slope  when  formed  by«  large  streams  with  a  fine- 
textured  load.  They  may  grow  to  great  size,  with  a 
radius  of  five  or  ten  miles,  in  large  valleys. 

Large  fans  drive  the  master  river  against  the  farther 
side  of  its  valley,  where  it  undercuts  the  valley  wall.  The 
fan  still  growing,  the  river  may  be  obstructed  and  thus 
required  to  spread  over  the  valley  floor  upstream  from 
the  fan,  forming  a  shallow  lake,  while  on  the  downstream 
side  the  river  descends  in  rapids  over  the  coarsest  bowlders 
brought  down  by  the-  torrent. 


198 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


How  many  fans  are  shown  in  Figure  94?  Where  has  their 
material  come  from?  How  has  it  been  brought?  What  effect 
have  they  on  the  course  of  the  main  river? 

A  torrent  frequently  changes  its  course  on  a  fan  and 

enters  the  main  river 
at  a  new  point.  Two- 
Ocean  creek,  a  small 
stream  in  the  Yellow- 
stone Park,  has  built 
a  fan  that  forms  a 
part  of  the  conti- 
nental divide.  Some- 
times the  stream  flows 
on  an  eastern  radius 
of  the  fan  to  Atlan- 
tic creek  (Missouri- 
Mississippi  system), 
sometimes  on  a  west- 
ern radius,  to  Pacific 
creek  (Columbia  sys- 
tem). 

Villages  are  often 
built  and  fields  are 
cultivated  on  fans  of 
large  size.  When  the  torrent  of  such  a  fan  is  turned  on 
a  new  course  it  may  flood  fields  and  villages,  causing  much 
damage.  A  valley  road  crossing  the  fan  is  swept  away 
where  the  torrent  then  comes  upon  it,  while  the  bridge 
over  the  former  channel  is  useless,  now  that  the  torrent 
has  abandoned  it. 


Fig.  94.    Alluvial  Fans 


MOUNTAINS 


199 


Accidents  of  this  sort  are  common  in  mountain  regions. 
In  1896  a  stream  entering  a  lake  in  Switzerland  overflowed 
its  fan  with  a  stony  flood  fed  by  a  landslip  in  the  head 
ravine.  It  laid  waste  a  strip  two  miles  long  and  over  300 
feet  wide  at  the  forward  end,  covering  it  with  a  layer  of 
stony  mud  ten  or  twelve  feet  thick.  Houses  were  pushed 
out  of  place;  a  road  and  a  railroad  were  buried.  The 
advance  of  this  curi- 
ous flood  was  some- 
times so  slow  that  the 
grass  on  the  fields  in 
front  of  it  was  saved 
by  hasty  mowing.  For 
a  time  all  travel  had 
to  go  by  boat  on  the 
lake.  The  people  who 
lived  on  the  fan  had 
some  compensation 
for  their  losses  in  car- 
rying the  thousands  of  visitors  to  and  from  the  scene  of 
the  disaster. 

Sometimes  the  steep  torrential  headwaters  wash  so  much 
waste  from  their  ravines  into  the  lower  valley  that  the 
river  is  unable  to  carry  along  all  that  it  receives.  Some 
of  the  waste  then  gathers  on  the  valley  floor,  gradually 
filling  it  higher  and  higher,  as  in  Figure  95.  Valley  floors 
of  this  form  are  much  more  easily  traveled  upon  than 
when  the  side  slopes  descend  directly  to  the  river  bank. 

After  mountain  waste  has  in  this  way  gathered  in  a  val- 
ley to  a  considerable  depth,  sometimes  measuring  several 


Fig.  95.    A  Filled  Valley  with  a  Flat  Floor 


200 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


hundred  feet,  there  may  be  a  decrease  in  the  amount  of 
waste  supplied  by  the  headwater  streams.  This  change 
will  permit  the  river  to  turn  part  of  its  strength  to  sweep- 
ing away  some  of  the  waste  in  its  bed,  and  thus  to  deepen 
its  channel.  As  more  and  more  waste  is  thus  removed, 
a  new  valley  comes  to  be  opened  in  the  flat  valley  floor, 
remnants  of  which  then  stand  in  benches  or  terraces  above 

the  new  level  of  the 
river,  as  in  Figure  96. 
Terraced  valleys  of 
this  kind  are  not  un- 
common in  the  Rocky 
mountain  region. 
Some  •  of  the  inner 
valleys  of  the  Hima- 
laya mountains  have 
gravel   terraces    over 

Fig.  96.    A  Terraced  Valley  1^^^    ^^et   high. 


119.  Lengthwise  and  Crosswise  Valleys.  — When  a  river 
has  cut  down  its  valley  floor  to  as  moderate  a  slope  as  the 
load  of  waste  that  it  has  to  carry  along  will  allow,  it  may 
still  wear  away  its  banks,  first  on  one  side,  then  on  the 
other.  Thus  in  the  course  of  time  the  river  broadens  the 
valley  floor.  This  is  especially  true  in  a  valley  that  is 
worn  down  along  a  belt  of  weak  rocks  parallel  to  the  gen- 
eral trend  of  a  mountain  range,  for  these  rocks  weather 
and  wash  away  at  a  comparatively  rapid  rate. 

The  crosswise  valleys,  by  which  the  rivers  of  the  long 
inner  valleys  find  outlets  through  inclosing  ridges,  are 


MOUNTAINS  201 

often  narrow  and  steep-walled  gorges,  for  the  ridge- 
making  rocks  are  resistant  and  weatlier  slowly.  The 
floor  of  a  crosswise  or  transverse  valley  may  be  hardly 
wider*  than  its  stream ;  the  walls  rise  steep  from  the 
water's  edge,  leaving  little  or  no  room  for  a  road  or  path 
on  either  side. 

It  is  chiefly  in  the  broader  lengthwise  valleys  that 
mountain  peoples  dwell.  When  the  outlet  valleys  are 
narrow  gorges  the  outer  world  has  for  centuries  been 
reached  only  by  passes  over  the  inclosing  ridges;  but 
modern  engineering  skill  has  sufficed  to  build  and  cut 
roads  and  railroads  through  many  gorges  that  were 
impassable  a  century  ago. 

120.    Earthquakes  of  Growing  Mountain  Ranges.  —  The 

process  of  bending  and  breaking  the  rock  structures 
within  a  mountain  mass  is  certainly  very  slow,  but  it 
sometimes  causes  sudden  snaps  and  slips  of  a  few  inches 
or  a  few  feet.  Tremors  then  spread  in  all  directions 
from  the  seat  of  disturbance,  diminishing  in  force  as  they 
advance.  On  reaching  the  earth's  surface  they  are  felt  as 
earthquakes,  producing  more  or  less  destruction.  Shocks 
of  this  kind  are  comparatively  common  in  and  near  most 
of  the  lofty  mountains  of  the  world. 

Earthquake  tremors  travel  through  the  earth's  crust  with 
great  velocity,  —  from  ten  to  forty  miles  a  minute  ;  but,  as 
in  the  case  of  water  waves,  the  actual  movement  of  the 
quaking  earth  at  any  point  may  be  only  a  few  inches  or  a 
few  feet  a  second,  backward  arid  forward.  The  shocks 
produced  by  earthquake  waves  are  most  violent  at  places 


202 


ELEMENTARY  PHYSICAL  GEOGRArHYT 


directly  over  the  seat  of  chief  disturbance.  They  may  be 
very  faint,  causing  no  damage.  They  may  be  strong 
enough  to  be  felt  violently  over  hundreds  of  square 
miles,  less  distinctly  over  many  thousands,  and  very  faintly 
(by  the  aid  of  delicate  instruments)  all  over  the  earth. 


Fig.  97.    Railroad  shaken  by  an  Earthquake,  Northeastern  India 

One  of  the  greatest  modern  earthquakes  occurred  at 
the  base  of  the  Himalaya  mountains  in  northeastern 
India  in  1897.  It  was  probably  caused  by  some  under- 
ground movement  of  mountain  growth.  It  formed  sev- 
eral fissures,  displacing  the  land  on  one  side  with  respect 
to  that  on  the  other,  forming  a  step  several  feet  high. 
The  vibrations  of  the  shock  loosened  rock  masses  and 
soil  on  steep  slopes,  causing  many  landslides,  which  left 


MOUNTAINS 


203 


the  hillsides  Ixire  and  clogged  the  valleys.  Thousands  of 
forest  trees  and  a  great  number  of  buildings  in  the  central 
area  were  broken  down  by  being  swayed  violently  back 
and  forth,  although  the  movement  was  only  a  few  inches. 
Streams  were  obstructed  and  turned  from  their  courses. 


Fig.  98 .- ..liace  displaced  b^ 


apan 


Railroad  tracks  on  the  neighboring  plains  were  thrown 
out  of  line. 

A  violent  earthquake  occurred  in  Japan  in  1891  by 
which  a  deep  fissure  was  formed  in  the  earth's  crust, 
and  the  land  on  one  side  of  it  was  lowered  with  respect 
to  that  on  the  other,  as  shown  in  Figure  98. 

Earthquakes  of  moderate  violence  are  still  frequent  in 
the  Alps,  occurring  five  or  ten  times  a  year.  Five  cen- 
turies  ago   (1348)   a  violent   earthquake   in   the  eastern 


204     ELEMENTARY  PHYSICAL  GEOGRAPHY 

Alps  caused  a  great  landslide  by  which  a  valley  was 
barred  across  and  a  lake  formed  upstream  from  the  slide. 
Countless  thousands  of  shocks  must  have  been  produced 
during  the  long  ages  of  mountain  growth.  The  associa- 
tion of  earthquakes  with  the  young  tilted-block  ridges  of 
Oregon,  with  the  more  mature  mountains  of  Nevada,  and 
with  vigorous  ranges  like  the  Alps  and  the  Himalayas,  is 
a  natural  result  of  the  continued  disturbance  or  growth  of 
the  mountains. 

121.  Human  Life  in  Lofty  Mountains.  —  The  people 
who  to-day  dwell  in  the  valleys  of  lofty  mountains  are 
in  many  cases  the  descendants  of  races  who  formerly 
occupied  the  adjacent  lower  lands,  from  which  they 
were  driven  by  conquering  invaders.  Inclosed  valleys 
among  mountains  serve  as  refuges,  where  pursuit  is  too 
difficult  to  be  profitable.  There  the  weaker  race  long 
remains  unmolested,  holding  little  intercourse  with  the 
outer  world  and  preserving  old  forms  of  speech  and  old- 
fashioned  customs.  The  invaders  occupy  the  neighboring 
open  country;  they  engage  in  traffic  with  other  parts  of 
the  world  and  advance  in  new  ways  of  living. 

122.  Subdued  Mountains.  —  There  are  certain  mountain 
ranges  of  moderate  height  in  which  sharp  peaks  are  absent 
and  bold  cliffs  are  rare.  The  slopes  are  of  moderate  steep- 
ness, and  rock  waste  covers  them  almost  from  base  to 
summit.  Mountains  of  this  kind  do  not  reach  upward 
into  a  climate  very  unlike  that  of  their  base;  and  if 
not  in  a  dry  or  a  frigid  region,  they  may  be  forest  clad 
to  the  top. 


MOUNTAINS  205 

The  earthquakes  that  are  common  in  mountains  of  active 
growth  and  the  landslides  that  happen  frequently  in  moun- 
tains where  the  valley  sides  are  still  steep  are  raCre  or 
unknown  in  these  mountains  of  gentler  form.  Unlike 
those  vigorous  and  lofty  younger  forms  in  which  uplift 
and  erosion  are  still  active,  the  rounded  forms  of  these 
mountains  express  subdued  strength,  as  if  their  high 
peaks  and  ridges  had  been  greatly  worn  away  by  the  long- 
continued  attack  of  the  weather.  They  may  therefore  be 
called  subdued  mountains. 

The  Blue  ridge  and  other  mountains  of  North  Carolina 
are  good  examples  of  subdued  mountains.  No  sharp  peaks 
tower  into  the  sky.  The  summits  generally  rise  dome- 
like in  rounded  outline.     Heavy  forests  clothe  their  slopes. 

Subdued  mountains  may  still  have  so  strong  a  relief 
that  the  people  living  in  their  valleys  preserve  older 
fashions  than  those  of  the  more  open  lower  country.  This 
is  seen  in  the  homespun  clothing  and  in  the  primitive 
manner  of  living  of  the  North  Carolina  mountaineers. 

The  mountains  of  Wales  make  another  group  of  sub- 
dued forms,  but  more  rugged  than  the  mountains  of  North 
Carolina.  Here  remain  some  of  the  descendants  of  the 
ancient  Britons  who  were  driven  from  the  more  open 
lowlands  of  eastern  and  central  England  by  Saxon  and 
Norman  invaders,  1000  or  1500  years  ago.  The  Welsh 
language,  therefore,  represents  the  original  language  of 
Britain,  while  the  English  language  is  a  compound  of  the 
speech  of  the  invading  peoples  from  the  continent.  The 
Scotch  highlanders  are  clannish  because  the  clans  have 
long  lived  in  secluded  glens  among  the  Highlands. 


206  ELEMENTARY  PHYSICAL  GEOGRAPHY 

123.  Worn-Down  Mountains.  —  In  certain  parts  -  of  the 
world  ancient  mountain  ranges  have  been  almost  com- 
pletely worn  away.  Their  disordered  rocks,  once  rising  in 
lofty  peaks  and  ridges,  and  perhaps  bearing  snow  fields  and 
glaciers,  have  been  reduced  to  an  almost  plain  surface,  little 
above  baselevel  and  everywhere  open  to  settlement.  Low- 
lands of  this  kind  are  called  peneplains  {pene,  almost). 


Fig.  99.    The  Piedmont  Belt,  Virginia 

The  Piedmont  belt  of  Virginia,  between  the  Blue  ridge 
and  the  coastal  plain,  is  in  many  respects  an  excellent 
example  of  a  worn-down  mountain  range.  It  is  a  pene- 
plain, not  monotonously  smooth,  but  undulating  in  graceful 
swells  between  gentle  depressions.  The  soil  is  deep,  fine, 
and  fertile,  and  the  district  is  very  generally  occupied  by 
farms.  The  height  to  which  the  rock  masses  once  rose 
above  the  present  surface  is  reasonably  estimated  as  at  least 
one  mile ;  it  may  have  been  two  or  three.  The  wearing 
down  of  these  ancient  mountains  to  the  rolling  plain  of 
to-day  has  required  an  enormously  long  period  of  time. 

It  often  happens  that  the  plain  surface  of  a  worn-down 
mountain  range  is  here  and  there  surmounted  by  rounded 


MOUNTAINS 


207 


hills  or  low  mountains,  1000  or  more  feet  high,  composed 
of  the  most  resistant  rocks  of  the  whole  region.  These 
hills  are  the  last  remnants  of  the  mountains  that  once 
towered  over  the  surface  of  to-day.  Several  hills  of  this 
kind  are  scattered  over  the  Piedmont  plain  of  Virginia, 
one  being  shown  in  Figure  99.     Such  remnant  hills  and 


Fig.  100.    Map  of  the  Piedmont  Belt,  Virginia 

mountains  are  often  called  monadnocks,  after  an  excellent 
example  of  their  class  in  southwestern  New  Hampshire. 

It  is  generally  the  case  that  old-mountain  lowlands  are 
now  uplifted  above  the  position  in  which  they  stood  when 
worn  down,  so  that  they  form  plateaulike  uplands.  Their 
streams  are  thus  revived  into  a  new  period  of  activity  and 
at  once  proceed  to  trench  and  dissect  the  upland. 

The  Piedmont  belt  of  Virginia  now  stands  several  hun- 
dred feet  above  baselevel.  It  is  cut  across  by  a  number 
of  active  streams  that  flow  in  rocky,  steep-sided  valleys 


208     ELEMENTARY  PHYSICAL  GEOGRAPHY 

from  100  to  300  feet  below  the  upland  plain.  It  must 
therefore  be  supposed  that  this  region  has  been  somewhat 
uplifted  since  its  ancient  mountains  were  worn  down.  It 
is  in  the  valley  sides  that  the  tilted  rock  structures  in  the 
foundations  of  the  ancient  mountains  are  best  seen. 

Southern  New  Hampshire  and  Vermont,  central  and  west- 
em  Massachusetts,  and  all  of  Connecticut  include  many 
uplands,  above  which  occasional  hills  and  low  mountains 


Fig.  101.    The  Upland  of  New  England,  with  Mt.  Monadnock  in  the 
Distance  and  a  Valley  in  the  Foreground 

rise,  and  below  which  numerous  open  valleys  are  worn. 
When  an  observer  stands  on  the  uplands  the  sky  line  is  seen 
to  be  comparatively  even.  If  the  valleys  were  in  imagina- 
tion filled  up  again  to  the  level  of  the  uplands,  the  worn- 
down  peneplain  of  the  ancient  mountains  of  New  England 
would  be  restored. 

The  peneplain  does  not  now  stand  so  low  as  when  it  was 
worn  down.  It  has  been  uplifted  into  a  slanting  position, 
so  that  it  slowly  rises  from  sea  level  at  Long  Island  sound 
to  a  height  of  from  1400  to  1600  feet  on  the  northern 
boundary   of   central   and  western   Massachusetts.     The 


MOUNTAINS 


209 


valleys  have  been  carved  because  the  old  lowland  has  been 
lifted  up.  They  are  shallow  near  the  coast,  but  deep  (800 
to  1000  feet)  in  the  interior,  where  the  upland  is  higher 
above  baselevel.  They  are  comparatively  narrow  where 
the  rocks  are  so  resistant  that  they  weather  slowly,  but 
wide  open  where  the  rocks  are  weaker.  The  chief  of 
the  wider  valleys   is   that   of   the   Connecticut   river,   a 


Fig.  102.    Valley  of  the  Deerfield  in  the  New  England  Upland 

broad  lowland  excavated  along  a  belt  of  relatively  weak 
sandstones. 

The  uplands  have  a  scattered  farming  population,  here 
and  there  gathered  in  small  villages.  The  larger  valleys 
contain  many  villages  and  cities,  and  guide  the  chief  roads 
and  railroads.  Here  is  gathered  the  more  active  manu- 
facturing and  commercial  population  of  New  England. 


210 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


124.  Old  Mountain  Ridges.  —  The  Allegheny  mountains 
of  Pennsylvania  and  Virginia  consist  of  a  number  of  nearly 
parallel  ridges  with  remarkably  even  crest  lines,  here  and 
there  cut  down  by  the  notches  or  water  gaps  of  streams 
and  rivers.    The  strata  of  these  mountain  belts  are  strongly 


Fig.  103.    Diagram  of  the  Allegheny  Mountains,  Pennsylvania. 

folded,  SO  that,  if  unworn,  they  would  rise  in  great  arches, 
as  in  the  background  of  Figure  103. 

But  it  is  now  so  long  since  the  strata  were  pressed 
into  folds  that  they  have  been  worn  down  to  a  low 
peneplain  at  the  level  of  the  dotted  line  AB,  in  the  fore- 
ground of  Figure  103.  The  peneplain  thus  formed  has 
been  uplifted  one  or  two  thousand  feet;  the  weaker 
strata  have  been  again  worn  down,  forming  open  valleys 
and    leaving    the    harder    strata    standing    in    relief,    as 


MOUNTAINS  211 

even-crested  ridges.  The  waste  from  the  open  valleys 
has  been  washed  out  through  the  notches  that  have  been 
slowly  cut  down  where  the  streams  flowed  across  the 
harder  strata. 

Plate  IX  shows  one  of  these  ridges  in  Maryland,  with 
a  notch  cut  through  it  by  a  branch  of  the  Potomac  river- 
How  many  notches  are  shown  in  Figure  103? 

125.  Embayed  Mountains.  —  If  a  mountain  range  near  a 
continental  border  is  lowered,  it  will  be  partly  covered  by 


Fig.  104.    Model  of  Embayed  Mountains 
Compare  Figures  60,  62,  and  104.     Compare  Figures  71  and  104. 

the  sea.  The  effect  thus  produced  will  be  similar  to  that 
observed  in  the  half-drowned  coastal  plain  already  described. 
The  valley  floors  and  mountain  flanks  will  be  submerged 
to  a  greater  or  'less  depth,  and  many  long  bays  will  enter 
between  outstretching  promontories  and  islands,  as  in 
Figure  104.  Islands  of  this  kind  are  called  continental 
because  of  their  close  relation  to  the  neighboring  land. 


212     ELEMENTARY  PHYSICAL  GEOGRAPHY 

The  coast  of  British  Columbia  and  southern  Alaska  is 
bordered  by  high  mountains,  into  whose  valleys  the  sea 
now  enters  in  long  and  deep  passages,  called  fiords.  Lat- 
eral ridges,  separated  from  the  mainland  by  water  chan- 
nels or  sounds,  stand  forth  as  islands.  A  navigable  "inner 
passage,"  well  protected  from  the  rough  water  of  the  open 
ocean,  is  thus  provided  for  steam  vessels.  The  steep  moun- 
tain sides,  descending  rapidly  beneath  the  sea,  generally 
offer  no  flat  ground  for  settlement ;  but  most  of  the  fiords 
now  contain  delta  plains  where  streams  enter  their  heads ; 
here  villages  find  convenient  sites. 

The  coast  of  Maine,  part  of  the  dissected  upland  in  the 
old  mountain  region  of  New  England,  has  been  partly  sub- 
merged, so  that  it  is  entered  by  many  long  arms  of  the 
sea  and.  fringed  by  many  islands.  Excellent  harbors  are 
thus  provided,  and  many  of  the  people  living  near  the 
coast  are  sailors  and  fishermen. 

QUESTIONS 

Sec.  108.  What  is  a  mountain  range?  a  mountain  chain? 
How  do  mountains  differ  from  plateaus?  What  is  the  action  of 
mountain-making  forces?  State  a  theory  of  their  origin.  How  do 
streams  affect  mountain  form  ?  To  what  two  processes  is  mountain 
form  due  ? 

109.  Describe  an  example  of  block  mountains.  Where  are  good 
examples  of  this  class  found?  How  has  the  form  of  these  moun- 
tains been  produced?  How  do  the  forms  of  several  blocks  vary? 
What  can  be  said  of  the  age  of  these  mountains?  Why  may  it  be 
believed  that  these  mountains  are  still  growing?  Describe  the 
drainage  oi  these  mountains.  Consider  the  climate  of  the  region. 
Describe  the  places  of  settlement. 


MOUNTAINS  213 

110.  Describe  the  dissected  ranges  of  Nevada.  Compare  them 
with  the  block  mountains  of  Oregon.  Are  the  Nevada  ranges  still 
growing?  Compare  the  climate  of  the  ranges  of  Nevada  and  of 
Oregon.  Describe  the  streams  of  the  Nevada  ranges.  Where  are 
settlements  found  among  these  ranges  ? 

111.  Where  are  the  Jura  mountains?  What  is  their  structure? 
How  have  these  mountains  been  produced  ?  How  is  their  structure 
related  to  their  form  ?  What  changes  have  been  produced  by  erosion  ? 
Describe  the  drainage  of  these  mountains.  Compare  the  side  ravines 
and  the  crossing  gorges.     State  the  location  of  villages  and  roads. 

112.  113.  Name  some  lofty  mountain  ranges.  Upon  what  two  pro- 
cesses does  the  form  of  these  mountains  depend  ?  Compare  the  import- 
ance of  land  sculpture  in  these  ranges  and  in  the  block  mountains  of 
Oregon.  Of  what  do  the  lofty  peaks  and  ridges  consist?  What 
becomes  of  the  waste  from  them?  What  is  the  origin  of  the  deep 
valleys  ?  Compare  the  domes  and  the  horns  of  the  Alps.  Compare 
the  Selkirk  range  of  Canada  and  the  Rocky  mountains  of  Colorado. 

114.  Compare  plains  and  mountains  as  to  variation  of  tempera- 
ture ;  of  rainfall ;  as  to  conditions  of  life.  Why  are  the  sources  of 
large  rivers  often  found  in  mountains  ? 

115.  •  How  do  mountains  act  as  barriers  ?  Compare  the  two  slopes 
of  the  equatorial  Andes  as  to  climate  and  vegetation.  What 
influence  is  exerted  on  climate  by  the  Sierra  Nevada  and  the  Rocky 
mountains  ?  What  is  the  chinook  wind  ?  the  foehn  ?  How  have 
the  Himalayas  acted  as  barriers  between  nations  ?  How  do  mountain 
ranges  serve  as  national  boundaries?  Give  examples.  Explain  the 
importance  of  passes.  How  are  roads  and  railroads  built  over  moun- 
tains ?     Give  an  illustration  of  mountains  as  an  obstacle  to  travel. 

116.  117.  What  are  avalanches?  How  are  they  caused?  How 
do  they  move  ?  How  are  villages  and  roads  protected  from  them  ? 
Describe  an  ice  fall  in  the  Alps.  What  is  a  landslide  ?  Describe 
the  landslide  of  Airolo  in  the  Alps;  of  the  upper  Ganges  in  the 
Himalayas.  What  disaster  followed  the  latter  landslide?  How 
were  its  dangers  lessened? 


214  ELEMENTARY  PHYSICAL  GEOGRAPHY 

118.  Describe  the  movement  of  rock  waste  in  mountains.  How 
is  the  form  of  the  waste  fragments  changed  ?  What  is  an  alluvial 
fan  ?  How  is  it  formed  ?  How  does  the  form  of  alluvial  fans  vary  ? 
How  do  fans  affect  the  course  of  a  river  in  front  of  them  ?  How 
does  the  course  of  a  torrent  vary  on  its  fan  ?  Describe  Two-Ocean 
creek.  To  what  dangers  are  villages  and  roads  on  fans  exposed? 
Describe  an  example  from  Switzerland.  Describe  and  explain  a 
waste-filled  valley.     Describe  and  explain  a  terraced  valley. 

119.  How  are  valleys  widened?  What  sort  of  valleys  are  wid- 
ened most  easily  ?  Describe  crosswise  valleys.  Compare  lengthwise 
and  crosswise  valleys  as  to  occupation. 

120.  What  is  an  earthquake  ?  How  are  earthquakes  related  to 
mountains?  How  fast  do  earthquake  tremors  travel?  How  much 
movement  may  they  cause?  Where  are  the  shocks  felt  most  vio- 
lently? How  far  may  they  be  felt?  How  often  do  earthquakes 
occur  in  the  Alps?  Describe  the  great  earthquake  of  India,  1897. 
What  effect  was  produced  by  an  earthquake  in  Japan  in  1891  ? 

121.  Compare  the  people  of  mountains  with  those  of  the  neigh- 
boring lowlands. 

122.  Describe  subdued  mountains  as  to  height,  form,  rock 
waste,  earthquakes,  landslides.  Describe  an  example  of  this  class. 
What  effects  have  these  mountains  on  their  inhabitants  ? 

123.  What  is  meant  by  worn-do\vn  mountains  ?  What  is  a  pene- 
plain? Describe  an  example  in  Virginia.  What  is  a  monadnock? 
Describe  and  explain  the  valleys  of  the  Virginia  Piedmont  belt. 
Describe  and  explain  the  uplands  and  valleys  of  southern  New 
England.     How  do  they  influence  the  distribution  of  population? 

124.  Describe  the  Allegheny  ridges  as  to  form ;  as  to  origin  ;  as 
to  drainage.     What  is  a  water  gap  ? 

125.  Describe  the  appearance  of  embayed  mountains.  What  is 
their  origin  ?  What  is  a  continental  island  ?  Describe  the  coast  of 
southern  Alaska  ;  the  coast  of  Maine. 


CHAPTER   VII 
VOLCANOES 

126.  Volcanic  Eruptions.  —  Most  of  the  processes  of 
nature  go  on  without  violence.  The  usual  movements 
of  the  winds  and  currents,  the  flow  and  ebb  of  the  tides, 
the  rise  and  fall  of  the  lands,  the  weathering  and  wash- 
ing of  rock  waste  are  so  placid  that  we  gain  confidence 
in  the  earth  as  a  safe  home  to  live  in.  But  sometimes 
natural  processes  of  a  more  violent  behavior  are  witnessed. 
Hurricanes  and  tornadoes  bring  destructive  winds  and  tor- 
rential rains,  flashes  of  lightning  and  peals  of  thunder. 
Landslides  rush  down  mountain  sides,  overwhelming  the 
valleys  below.  Now  and  then  the  rocky  crust  beneath 
us  quivers  and  trembles  in  earthquakes.  Great  waves 
occasionally  roll  in  from  the  sea  and  sweep  over  low 
coastal  lands.  Here  and  there  volcanoes  burst  forth 
with  terrible  commotion.  Nature  then  seems  frightful 
and  destructive.  Those  who  are  overtaken  by  such  dis- 
asters struggle  against  them,  hopefully  awaiting  the  return 
of  the  more  peaceful  conditions  under  which  their  habits 
of  life  have  been  formed,  for  man  could  not  survive  if 
he  were  always  battling  against  the  wilder  forces  of 
nature. 

Of  all  natural  catastrophes,  the  explosive  eruption  of 
a  great  volcano  is  the  most  terrible.     The   air  resounds 

215 


216  ELEMENTARY  PHYSICAL  GEOGRAPHY 

with  its  roaring.  The  sky  is  darkened  and  the  sun  is 
hidden  by  clouds  of  dust  blown  from  the  crater.  The 
sea  is  burdened  with  floating  ashes.  Glowing  streams  of 
molten  rock,  or  lava,  flow  down  the  flanks  of  the  volcano, 
driving  away  everything  that  can  take  flight  before  them. 
Even  the  earth  around  trembles  as  the  gases  and  lavas 
burst  out  from  their  deep  sources.  No  wonder  that  igno- 
rant races  of  men  have  imagined  struggling  giants  to  be 
imprisoned  under  active  volcanoes,  nor  that  even  the  most 
learned  are  baffled. when  trying  to  account  for  these  ter- 
rific displays  of  natural  forces. 

But  violent  as  a  volcanic  eruption  may  be,  it  weakens 
and  in  time  ceases.  The  sky  clears,  the  sun  shines  again, 
and  nature  once  more  goes  on  with  her  more  quiet  tasks. 
As  the  years  pass  by  and  a  soil  is  formed  on  the  weath- 
ered lavas,  plants  clothe  their  surface  and  man  comes  to 
dwell  on  the  flanks  of  the  volcanic  mountain.  The  erup- 
tion is  forgotten ;  fields  and  villages  occupy  the  volcanic 
slopes ;  little  remains  to  tell  of  the  commotion  of  former 
times. 

127.  Young  Volcanoes.  —  Volcanoes  are  formed  by  the 
ascent  of  molten  lava  through  fractures  or  passages  lead- 
ing from  unknown  depths  beneath  the  earth's  crust  to  its 
surface,  on  the  land  or  on  the  sea  floor.  Although  the 
lava  is  very  hot,  it  is  not  burning  or  flaming.  A  volcano 
should  never  be  described  as  a  burning  mountain. 

It  is  believed  by  many  that  the  ascent  of  molten  lava 
from  its  deep  source  is  chiefly  caused  by  pressures  similar 
to  those  which  cause  movements  in  the  earth's  crust  in 


VOLCANOES 


217 


mountain  building.  As  the  lava  nears  the  surface  and  meets 
water  in  greater  or  less  quantities,  explosions  of  steam  and 
other  heated  gases  take  a  violent  part  in  the  eruptions. 


~  I  -^"-      ■    ■  !!■    I    I  '    '      llllV'MII     '''-"-     1V"       III  I  ■■■     s^M 


Fig.  105.    Vesuvius  in  Eruption 


The  early  growth  of  a  volcano  has  occasionally  been 
observed.  The  outburst  is  preceded  and  accompanied  by 
earthquakes,  which  indicate  the  breaking  of  an  upward  pas- 
sage through  the  underground  rocks,  before  hot  lavas  make 
their  appearance  at  the  surface.     When  the  eruption  is 


218 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Fig.  10(3.    Monte  Nuovo 


accompanied  by  gaseous  explosions  much  of  the  lava  is 
blown  into  fragments,  of  which  the  smaller  are  called 
ashes  or  cinders.  The  larger  blocks  and  the  coarser 
ashes  accumulate  in  a  conical  heap,  or  volcano,  frequently 
having  remarkable  regularity  of  form,  a  cup-shaped  hollow 
or  crater  being  kept  open  at  the  top  over  the  vent  by 
the  outbursting  gases.     The  finer  ashes  or  dust  may  fall 

far  away.  When  the 
eruption  is  less  vio- 
lent   the    lava  runs 
forth  more  quietly  in 
a  stream  or  flow,  fol- 
lowing the  slopes  of 
the  ground.     Explo- 
sive and  quiet  erup- 
tions may  alternate  in  irregular  succession,  and  after  many 
eruptions  the  volcano  may  become  a  lofty  mountain,  one 
or  two  miles  high. 

Monte  Nuovo  (new  mountain)  is  a  small  volcano  that 
was  formed  on  the  north  side  of  the  Gulf  of  Naples 
in  Italy  in  1538.  Earthquakes  occurred  thereabouts 
for  two  years  before  the  eruption,  when  in  a  week's 
time  a  cone  was  built  up  440  feet  high,  half  a  mile  in 
diameter  at  the  base,  and  with  a  crater  over  400  feet 
deep.  Masses  of  lava  "  as  large  as  an  ox "  were  shot 
into  the  air  by  the  bursting  of  great  bubbles  of  gas  or 
steam  that  ascended  through  the  lava  in  the  vent.  Finer 
ashes  fell  over  the  country  for  several  miles  around. 
The  people  of  the  neighboring  villages  fled  in  terror 
from  their  homes. 


VOLCANOES  219 

A  greater  eruption  took  place  in  Mexico  in  1759,  when 
the  volcano  JoruUo  (pron.  Ho-rul-yo)  was  built  on  the 
central  plateau,  burying  fertile  fields  of  sugar  cane  and 
indigo.  The  outburst  was  preceded  by  earthquakes ;  the 
eruption  continued  half  a  year,  building  six  cones  and 
pouring  out  extensive  lava  flows.  The  highest  cone, 
Jorullo,  rose  700  feet  above  the  plateau.  The  flows 
retained  a  perceptible  heat  for  over  twenty  years. 

Many  examples  might  be  given  of  marine  eruptions. 
In  1867  a  shoal  was  discovered  among  the  Tonga  islands 
of  the  Pacific  (lat.  20°  20'  S.,  long.  175°  20'  W.),  the 
surrounding  sea  floor  being  about  1000  fathoms  deep.  In 
1877  smoke  was  seen  ascending  from  the  sea  surface  over 
the  shoal.  In  1885  an  island  had  been  formed  two  miles 
long  and  200  feet  high.  At  this  time  a  terrific  eruption 
was  in  progress,  and  the  shocks  of  the  explosions  were  felt 
on  neighboring  islands.  As  the  island  consisted  chiefly 
of  ashes,  it  has  since  been  rapidly  eroded  by  the  waves 
and  will  soon  disappear,  unless  new  eruptions  occur. 

Most  volcanoes  have  not  been  observed  in  their  early 
growth,  yet,  even  if  not  now  in  eruption,  so  perfectly  do 
they  correspond  in  form  and  structure  with  such  examples 
as  Monte  Nuovo  and  Jorullo  that  no  doubt  can  remain  as 
to  their  origin. 

In  northern  California  there  is  a  cinder  cone  of  remark- 
ably perfect  form.  Its  barren  slopes  of  loose  ashes  rise 
640  feet  to  the  rim  that  incloses  a  crater  240  feet  deep. 
A  stream  of  lava  has  issued  from  near  the  base  of  the  cone, 
flooding  a  neighboring  valley  with  a  lava  field  a  mile  wide 
and  nearly  three  miles  long.     The  surface  of  the  field  is 


220 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


so  covered  with  unweathered  angular  blocks  of  lava  as  to 
be  almost  impassable.  The  edge  of  the  field  is  a  steep 
and  ragged  slope  100  feet  high.  It  obstructs  a  stream  from 
the  south,  which  forms  Snag  lake,  so  called  from  the  dead 
trees  still  standing  in  it.  On  all  sides  the  surface  of  the 
country  is  covered  with  a  layer  of  volcanic  ashes  and  dust, 
six  or  more  feet  deep  near  the  cone,  thinner  and  finer 
fai'ther  away,  yet  recognizable  at  a  distance  of  eight  miles. 


Fig.  107.    Cinder  Cone  and  Lava  Flow,  California 

From  the  size  of  trees  growing  on  the  ashes  it  is  estimated 
that  the  cinder  cone  was  built  about  200  years  ago.  The 
lava  flow  is  younger,  but  none  of  the  Indians  or  early 
settlers  thereabouts  (1845)  observed  its  eruption. 

128.  Great  Volcanoes.  —  Many  large  volcanoes,  whose 
first  eruption  must  have  occurred  many  thousands  of  years 
ago,  are  still  active.  After  long  periods  of  more  or  less 
complete  rest  they  burst  forth  again  for  a  short  time, 
blowing  out  showers  of  ashes,  building  their  cones  to  a 
height  of  10,000  feet  or  more,  and  adding  new  lava  streams 
to  their  flanks,  so  as  to  gain  a  diameter  of  ten  or  twenty 
miles  or  more  at  the  base.     The  melted  lava  often  breaks 


VOLCANOES 


221 


forth  from  the  mountiiin  side  and  flows  down  to  gentler 

slopes  on  the  flanks  and  out  upon  the  surrounding  country ; 

thus  the  cone  as  a  whole  comes  .-•-—. 

to  have  a  rudely  bedded  struc- 
ture of  ashy  and  dense  lavas. 
It  sometimes  happens  that 

the  upper  part  of  a  volcano  is 

destroyed  by  a  violent  eruption 

or  broken  in  by  underground 

disturbance,  forming  a  greatly 

enlarged    crater,    or    caldera. 

Volcanoes  of  this  form  are  some- 
times called  ring  mountains. 
Deception    island,    in    the 

South  Shetland  group,  beyond 

Cape  Horn,  is  the  high  rim  of 

a  caldera,  breached  on  one  side 

by  a  narrow  gap,  which  gives  entrance  to  a  quiet  circular 

bay.  Layers  of  ice 
are  to  be  seen  between 
beds  of  ashes  and  lava 
on  the  caldera  walls. 
The  cone  of  Vesu- 
vius has  been  built  in 
a  large  caldera  of  more 
ancient  origin.  The 
cone  buries  one  side  of 

the  caldera  rim,  the  other  side  being  known  as  Monte  Somma. 

Draw  a  map  of  Vesuvius  and  Monte  Somma,  like  the  map  of 
Deception  island  in  Figure  108. 


Fig.  108.    Deception  Island,  a  Vol- 
canic Caldera  (plan  and  section) 


Fig.  109.    The  Cone  of  Vesuvius  in  the  Caldera 
of  Monte  Somma  (looking  north) 


222 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Mt.  Mazama,  a  superb  ring  mountain  in  Oregon,  con- 
tains a  beautiful  lake  in  its  huge  caldera.  This  volcano 
must  have  been  once  several  thousand  feet  higher  than  it 
is  now,  before  its  upper  part  was  engulfed  in  the  formation 
of  the  caldera. 

Figures  110  and  115  are  maps  of  Mts.  Mazama  and  Shasta,  in  which 
the  mountain  form  is  indicated  by  lines  that  curve  around  the  slopes 
at  definite  heights,  every  line  following  a  level  course,  and  every  pair 


Fig.  110.    Contour  Map  of  Crater  Lake  in  Mt.  Mazama,  Oregon 


of  lines  differing  in  height  by  a  fixed  amount.  Lines  of  this  kind 
are  called  contour  lines,  and  the  maps  are  contour  maps.  Where  the 
lines  are  open  spaced,  the  slopes  are  relatively  gentle;  where  the  lines 
are  close  together,  the  slopes  are  steep.  Compare  the  inward  and  out- 
ward slopes  of  the  ring  of  Mt.  Mazama ;  compare  the  upper  and  lower 
slopes  of  Mt.  Shasta.  Determine  from  Figure  110  the  diameter  of  the 
caldera,  and  the  average  height  of  its  rim  above  sea  level  and  above  the 
lake  surface. 


VOLCANOES  223 

A  rough  classification  of  volcanoes  groups  them  as 
active,  when  they  are  frequently  in  eruption ;  dormant 
(sleeping),  when  now  at  rest,  though  giving  signs  in  hot 
springs  and  sulphurous  vapors  that  activity  may  be  begun 
again;  and  extinct,  when  they  give  no  sign  of  activity. 
It  is  not  possible  to  make  certain  distinction  between  the 
last  two  classes. 

Showers  of  ashes  as  they  chance  to  fall  may  bury  villages, 
fields,  and  forests.  The  disturbance  in  the  atmosphere  dur- 
ing a  violent  eruption  often  causes  rainfall.  The  floods 
thus  caused  may  be  increased  by  the  water  from  melted 
snow  on  a  lofty  cone,  and  occasionally  by  hot  water  from 
the  crater  itself.  The  tremendous  eruption  of  Galung- 
gung,  Java,  in  1822,  produced  hot  and  muddy  torrents 
which  devastated  villages  and  plantations  on  the  lowlands. 

At  the  eruption  of  Conseguina,  Central  America,  in 
1835,  ashes  destroyed  trees  and  dwellings  twenty-five  miles 
south  of  the  volcano ;  thousands  of  cattle  and  innumerable 
wild  animals  and  birds  were  killed.  Lava  blocks  in  frag- 
ments five  or  more  feet  in  diameter  are  strewn  for  ten  or 
fifteen  miles  around  the  great  cone  of  Cotopaxi,  Ecuador. 

An  explosive  eruption  of  Moimt  Pelee  on  the  island  of 
Martinique,  in  the  Lesser  Antilles,  took  place  in  May, 
1902.  Clouds  of  dust  and  ashes  were  driven  out  by  great 
volumes  of  heated  gases.  The  city  of  St.  Pierre,  on  the 
coast  about  six  miles  southwest  of  the  crater,  was  suddenly 
overwhelmed,  and  nearly  all  of  its  inhabitants  —  probably 
over  20,000  persons — were  killed. 

The  first  recorded  eruption  of  Vesuvius,  a.d.  79,  dark- 
ened the  sky  with  its  clouds.    The  ancient  city  of  Pompeii 


224 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


was  buried  in  ashes  and  about  2000  persons  (estimated  at 
one  fifteenth  of  the  population)  were  killed.  Herculaneum, 
near  by,  was  overwhelmed  with  torrents  of  ashy  mud. 
After  being  long  forgotten  and  overgrown  by  modern 


Fig.  111.    Excavations  in  Herculaneum 

villages,  parts  of  these  cities  have  been  laid  bare  by  recent 
excavations,  affording  many  illustrations  of  ancient  archi- 
tecture and  of  ancient  modes  of  living.  The  walls  in  the 
foreground  of  Figure  111  are  the  ruins  of  houses  in  ancient 
Herculaneum.     They  were  buried  to  the  level  LL. 

129.  Earthquakes  in  Volcanic  Districts. — The  shocks  of  a 
violent  eruption  may  shatter  the  volcano,  breaking  its  sides. 


VOLCANOES  225 

The  earthquakes  thus  caused  are  felt  for  many  miles  around 
the  volcano.  The  exploding  gases  produce  thundering 
sounds,  sometimes  audible  for  hundreds  of  miles. 

In  the  remarkable  explosion  of  the  volcanic  island  of 
Krakatoa,  already  referred  to  (page  27),  half  the  island  was 
destroyed,  leaving  water  more  than  1000  feet  deep  where 
high  land  had  stood  before.  The  air  was  shaken  so  vigor- 
ously by  the  explosion  that  windows  were  broken  a  hun- 
dred miles  away.  Huge  sea  waves  rolled  away  from  tlfe 
exploded  island,  causing  great  destruction  on  neighboring 
coasts.  Pumice,  or  light  spongy  lava,  formed  a  floating 
layer  on  the  sea  surface,  obstructing  the  course  of  vessels. 
The  dust  blown  out  of  the  volcano  darkened  the  air  for 
hundreds  of  miles  aroimd.  As  the  dust  was  spread  far 
and  wide  by  the  upper  atmospheric  currents,  it  increased 
the  brilliancy  of  sunset  and  sunrise  colors.  The  famous 
"  red  sunsets  "  thus  produced  were  visible  in  all  parts  of 
the  world  before  the  end  of  1883 ;  then,  as  the  dust  settled, 
their  brilliancy  gradually  decreased. 

Besides  the  earthquakes  directly  produced  by  the  explo- 
sive eruptions  of  volcanoes,  it  is  probable  that  many  other 
earthquakes  in  volcanic  districts  are  the  result  of  disturb- 
ances within  the  crust  of  the  earth  not  directly  connected 
with  volcanic  action.  The  numerous  earthquakes  of  Japan 
and  Italy  sometimes  accompany  eruptions,  but  are  more 
frequently  independent  of  all  visible  eruptive  action. 

Great  destruction  is  caused  by  earthquakes  in  regions 
that  are  frequently  shaken.  In  the  thickly  populated  dis- 
tricts of  southern  Italy  many  thousands  of  lives  have  been 
lost  in  the  violent  earthquakes  of  the  last  three  centuries. 


226  ELEMENTARY  PHYSICAL  GEOGRAPHY 

130.  Distribution  of  Volcanoes.  —  Volcanoes  generally 
occur  near  the  seacoast  or  on  the  sea  floor,  but  a  considerable 
number  of  cones  and  flows  are  known  far  in  continental 
interiors.  Volcanoes  are  more  numerous  on  the  lands  bor- 
dering the  Pacific  ocean  and  the  mediterranean  seas  than 
on  the  coasts  of  the  Atlantic,  but  many  volcanic  islands  are 
known  in  the  Atlantic,  as  well  as  in  the  Pacific  and  Indian 
oceans.  It  is  estimated  that  over  300  volcanoes  are  now 
active,  about  100  of  these  standing  on  the  continents.  All 
high  islands  of  small  area,  far  from  the  continents,  and  many 
such  islands  near  the  continents  are  of  volcanic  origin. 

Extinct  volcanoes  are  sometimes  found  far  inland. 
Cinder  cones  and  barren  lavas  are  known  on  the  plateaus 
of  Arizona,  300  miles  from  the  ocean;  in  Colorado,  800 or 
more  miles  inland;  in  Tibet,  500  or  more  miles  inland. 
Several  active  volcanoes  in  Mexico,  Central  America,  and 
elsewhere  are  so  far  from  the  coast  that  direct  connection 
with  sea  water  should  not  be  regarded  (as  it  has  been) 
necessary  to  eruptions. 

Active  volcanoes  in  the  interior  of  continents  are  rare, 
but  a  large  one  is  known  in  central  Africa,  north  of  Lake 
Tanganyika,  700  miles  from  the  Indian  ocean. 

Islands  formed  by  the  growth  of  volcanoes  in  mid  ocean 
are  often  bordered  by  wave-cut  cliffs,  so  that  it  is  almost 
impossible  to  find  a  landing  place  on  their  shores.  Being 
of  rugged  form  and  nearly  inaccessible,  as  well  as  distant 
from  the  continents,  they  are  all  the  more  lonesome. 

A  remarkable  instance  of  the  effect  of  isolation  on  the 
occupants  of  a  remote  volcanic  island  is  seen  in  the  language 
of  the  people  of  Iceland.     Icelandic,  Norwegian,  Swedish, 


.»,.J^"l«.t-\'l ,1, —  ?  1 


VOLCANOES 


227 


and  Danish  were  all  one  language  a  thousand  years  ago ; 
but  while  the  isolated  Icelandic  has  preserved  its  ancient 
form  with  slight  change,  the  languages  of  the  continental 
countries  have  been  much  modified ;  that  of  Denmark 
especially  havifig  been  affected  by  the  neighborhood  of 
Germany. 

131.  Lava  Flows.  —  Great  flows  of  lava  sometimes 
run  beyond  the  base  of  the  volcano  in  which  they  break 
forth.     Their  surface  is  comparatively  smooth  if  it  remains 


Fio.  113.    Lava  Flows  on  the  Plateaus  of  Arizona 


unbroken  after  first  cooling,  but  extremely  ragged  and 
angular  if  the  first  crust  is  repeatedly  broken  by  con- 
tinued movement.  The  edge  of  a  ragged  flow  may 
form  a  bluff  100  feet  or  more  in  height.  On  one  of  the 
plateaus  of  Arizona  near  the  Colorado  canyon  stands  a 
throng  of  volcanic  cones,  from  which  broad  streams  of 
lava  descend  the  bordering  cliffs  in  black  cascades  and 
form  barren  lava  floods  on  a  lower  plateau  near  by. 


228  ELEMENTARY  PHYSICAL  GEOGRAPHY 

In  1783  a  great  flood  of  lava  rose  from  a  deep  fissure 
in  Iceland,  the  lava  issuing  tranquilly  for  the  most  part, 
flowing  away  in  vast  sheets  on  each  side,  and  advancing 
in  streams  far  along  the  lower  valleys.  Hundreds  of 
small  cones  were  built  over  the  fissure,  which  was  twenty 
miles  long.  In  the  course  of  ages  successive  lava  floods 
of  this  kind  have  built  up  broad  uplands  in  the  plateau  of 
Iceland,  the  loose  slaggy  cones  of  earlier  eruptions  being 
gradually  buried  under  later  sheets. 

•Two  lava  streams  of  the  eruption  of  1783  in  Iceland 
flowed  down  valleys  forty-five  and  fifty  miles  from  their 
source,  gaining  a  depth  of  several  hundred  feet  where  the 
valleys  were  narrow,  and  spreading  out  in  lakelike  plains 
where  the  valleys  were  open.  The  water  of  side  streams 
was  dammed  and  rose  in  lakes.  Twenty  villages  were 
destroyed  by  the  floods  of  lava  or  water;  9000  persons 
(about  one  seventh  of  the  island's  population)  and  a  great 
number  of  cattle  perished,  not  only  at  the  time  of  the 
eruption,  but  afterward  during  a  famine  caused  by  the 
burial  of  the  pastures  and  by  the  desertion  of  the  coast 
by  fish. 

The  form  assumed  by  successive  lava  flows  in  building 
a  plateau  is  sometimes  imitated  on  a  cold  winter  night 
when  trickling  streams  of  water,  supplied  by  daytime 
thawing,  are  frozen  as  they  advance.  If  the  water  is  arti- 
ficially colored,  successive  flows  are  made  plainly  visible. 

Lava  floods  thousands  of  square  miles  in  area  have 
been  poured  forth  in  Idaho,  Oregon,  and  Washington, 
where  they  form  an  extensive  plateau  in  a  broad  depres- 
sion among  the  surrounding  mountains. 


VOLCANOES 


229 


Between  the  Columbia  and  Snake  rivers,  in  eastern 
Washington,  the  plain  surface  of  the  lava  flood  meets  the 
inclosing  mountains  just  as  the  sea  meets  a  half-drowned 
mountain  range.  The  lava  forms  level  bays  between  the 
ridges ;  the  ridges  stand  forth  like  promontories;  outstand- 
ing peaks  rise  like  islands  over  the  plain.  A  rugged  moun- 
tainous basin  has  thus  been  converted  into  a  plateau.  Part 
of  the  lava  plain  has  been  uplifted  in  domelike  form  to  a 
greater  height  than  the  rest  and  is  now  deeply  dissected 
by  the  canyons  of  Snake 
river  and  its  branches. 
This  part  is  called  the 
Blue  mountains,  j5,  Fig- 
ure 114. 

132.  Dissected  Volca- 
noes.— ^Torrential  streams 
running  down  the  slope 
of  volcanic  cones  carve 
ravines  on  their  flanks. 
Many  ravines  are  formed 
during  the  periods  of  rest  in  the  growth  of  great  volcanoes, 
only  to  be  .filled  again  by  later  eruptions  of  lavas  and 
ashes.  After  eruptions  cease  the  ravines  deepen  more  and 
more,  leaving  sharp  ridges  between  them,  and  at  last  dis- 
secting the  cone  so  deeply  as  to  leave  little  appearance  of 
its  original  shape. 

Mt.  Shasta,  in  northern  California,  is  furrowed  on  all 
sides  by  gigantic  ravines,  but  its  conical  form  is  still  well 
preserved.  Figures  115,  116.     Many  meadows  about  its 


Fig.  114.    The  Lava  Plateau  of  Idaho, 
Oregon,  and  Washington 


280 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


base  mark  the  sites  of  lakes  formed  by  lava-flow  barriers 
but  now  filled  and  drained.  The  best  agricultural  land 
in  the  region  is  of  this  origin. 


Fig.  115.    Contour  Map  of  Mount  Shasta,  California 

A  number  of  extinct  and  more  or  less  dilapidated  vol- 
canic cones  surmount  the  plateaus  of  Arizona  and  New 
Mexico,  Mts.  San  Francisco  and  Taylor  being  among  the 
best  examples. 

Before  the  summit  of  Mt.  Mazama  was  destroyed  by 
engulfment  its  height  was  probably  about  equal  to  that 


VOLCANOES 


231 


of  Mt.  Shasta  to-day.  Ravines  like  those  of  Shasta  had 
been  worn  down  the  slopes  of  Mazama;  their  lower 
courses  are  still  seen  on  the  outer  slopes  of  the  ring 
mountain,  but  their  upper  courses  are  lost. 

Many  great  volcanoes  in  various  stages  of  activity  and 
dissection  are  found  in  the  Andes  along  the  western  side 
of  South  America. 


Fig.  IKJ.     Mount  Shasta 

133.    Geographical  Changes  caused  by  Volcanoes.  —  The 

construction  of  large  volcanoes  by  successive  eruptions 
sometimes  causes  curious  changes  in  the  course  of  rivers, 
whose  valleys  are  more  or  less  blockaded  by  the  new-built 
cones. 

A  remarkable  example  of  this  kind  is  foimd  in  Central 
America,  where  the  growth  of  a  range  of  volcanoes  has 
transformed  a  bay  that  once  opened  to  the  Pacific  into  a 
lake,  known  as  Lake  Nicaragua.    The  volcanoes  formed  so 


232 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


effective  a  barrier  that  the  lake  surface  is  now  105  feet 
above  sea  level  and  its  outlet  flows  across  what  used  to 
be  the  continental  divide  and  discharges  into  the  Carib- 
bean sea.     Since  the  outlet  took  this  course  it  has  eroded  a 


Fig.  117.    Map  of  the  Lake  Nicaragua  District 

deep  gorge  across  the  divide,  and  the  level  of  the  lake  is 
now  lower  than  when  the  eastward  overflow  first  took  place. 
This  lake  would  form  part  of  the  proposed  interoceanic 
canal  route  across  Nicaragua. 

Draw  a  map,  based  on  Figure  117,  to  show  the  general  outline  of 
the  land  before  the  volcanic  range  was  built.  The  original  outline 
of  the  bay  now  closed  by  the  volcanoes  and  their  lava  flows  is  shown 
by  a  dotted  line.  Describe  the  changes  caused  by  the  building  of 
the  volcanic  range. 


VOLCANOES  233 


QUESTIONS 

Sec.  126.  Give  examples  of  the  quiet  processes  of  nature;  of  the 
violent  processes.     Describe  the  explosive  eruption  of  a  volcano. 

127.  How  are  volcanoes  formed?  What  is  the  most  probable 
cause  of  the  ascent  of  lava  in  volcanoes  ?  What  is  the  effect  of 
steam  ?  Describe  the  early  growth  of  a  volcano.  Give  an  example 
from  near  Naples ;  from  Mexico  ;  in  the  Pacific.  Describe  the  cin- 
der cone  in  California.  How  did  its  lava  flow  affect  a  neighboring 
stream  ?     Why  is  this  volcano  thought  to  be  of  recent  origin  ? 

128.  How  are  great  volcanoes  formed?  What  size  do  they 
attain  ?  What  is  a  caldera  ?  Describe  Deception  island  ;  Vesuvius 
and  Monte  Somma ;  Mt.  Mazama  and  its  caldera.  How  may  volcanoes 
be  classified  ?  What  effects  may  be  produced  by  showers  -of  ashes  ? 
by  floods?  How  may  these  floods  be  caused?  Describe  some  inci- 
dents of  the  eruption  of  Galung-gung,  1822;  of  Cons6guina,  1835; 
of  Cotopaxi ;  of  Pelee,  1902. 

129.  Why  are  earthquakes  often  associated  with  volcanoes? 
Describe  the  explosion  of  Krakatoa. 

130.  How  are  volcanoes  distributed?  Compare  the  Atlantic  and 
Pacific  in  this  respect.  How  many  active  volcanoes  are  known? 
How  many  of  these  are  on  the  continents?  Where  are  volcanic 
islands  found  ?  What  forms  have  they  ?  Where  are  extinct  vol- 
canoes often  found  ?  Where  is  an  active  volcano  found  far  inland  ? 
Give  an  instance. of  the  effects  of  living  on  a  remote  volcanic  island. 

131.  Describe  the  surface  form  of  lava  flows.  Describe  the  lava 
cascades  near  the  Colorado  canyon ;  the  eruption  and  lava  flood  of 
1783  in  Iceland ;  the  lava  floods  of  Idaho. 

132.  Describe  a  dissected  volcano.  Name  some  examples  of  this 
class.     Compare  Mts.  Shasta  and  Mazama. 

133.  What  geographical  changes  may  be  produced  by  volcanoes  ? 
Describe  an  example  of  such  changes  in  Nicaragua. 


CHAPTER    VIII 
RIVERS  AND   VALLEYS 

134.    Underground  Water The  water  supplied  by  rain 

and  snow  is  disposed  of  in  part  by  evaporating  from  the 
surface,  in  part  by  running  down  the  slopes  of  the  land 
to  the  streams,  and  in  part  by  sinking  underground.  The 
latter  part  is  called  underground  water,  or  simply  ground 
water. 

The  proportions  of  these  several  parts  vary  under 
different  conditions.  The  greater  part  of  a  light  and 
long-continued  rain  may  pass  underground,  especially  if 
falling  on  a  plain.  A  very  heavy  rain,  or  "  cloud-burst," 
falling  on  strong  slopes  is  largely  disposed  of  by  direct 
run-off,  causing  sudden  floods. 

Rain,  falling  on  a  surface  having  a  deep  soil  well  cov- 
ered with  vegetation  (grass,  bushes,  or  forest),  will  for  the 
most  part  soak  into  the  ground.  On  arid  plains  a  great 
part  of  a  light  rain  may  dry  off  from  the  barren  surface  of 
the  ground,  but  a  heavy  rain  will  run  off  in  a  flood. 

Loosely  consolidated  strata  and  deep  rock  waste  take 
in  much  ground  water.  Firm  rocks,  such  as  granites, 
allow  but  little  water  to  enter  beneath  the  weathered 
waste  on  their  surface.  When  the  ground  is  frozen  little 
water  can  enter  it ;  hence  rivers  rise  in  floods  when  deep 
snow  is  rapidly  melted  by  a  heavy  rain. 

234 


RIVERS  AND  VALLEYS 


235 


Underground  water  is  essential  to  the  growth  of  plants, 
whose  roots  must  reach  moist  earth.  Where  grass  and 
trees  cover  the  surface,  much  groimd  water  taken  in  by 
their  roots  is  discharged  into  the  air  by  evaporation  from 
their  leaves. 


Fig.  118.    Diagram  of  Cavern  and  Sink  Hole 


135.  Caverns.  —  Most  rocks  are  not  soluble  in  water. 
Limestone  is  exceptional  in  this  respect ;  it  may  be  slowly 
dissolved,  especially 
by  ground  water, 
which  gathers  cer- 
tain acids  from 
decomposing  vege- 
tation as  it  soaks 
down  through  the 
soil.  Caverns  in 
limestone     districts 

are  the  result  of  this  solvent  action  of  underground  waters. 
The  Mammoth  cave  of  Kentucky  and  the  Luray  cavern  of 
Virginia  are  famous  examples  of  their  class.  Streams 
/  gathering  on  the  surface  descend  to  underground  pas- 
(  sages  by  hollows,  known  as  sink  holes  or  swallow  holes. 
After  flowing  underground  for  some  distance  such  streams 
may  issue  in  enlarged  and  tUrbid  currents  from  the  mouths 
of  caverns. 

Where  sink  holes  and  cavern  drainage  prevail  so  much 
water  enters  the  ground  that  surface  streams  are  compara- 
tively rare.  When  the  sink  holes  or  the  underground  pas- 
sages become  obstructed  ponds  and  lakes  are  formed  in 
the  surface  basins. 


236  ELEMENTARY  PHYSICAL  GEOGRAPHY 

Several  species  of  animals  dwelling  in  the  complete 
darkness  of  caverns  are  blind,  but  their  senses  of  hearing 
and  touch  are  highly  developed. 

As  the  cavern  enlarges,  its  roof  may  fall  in  more  or  less 
completely.  The  beautiful  Natural  bridge  of  Virginia  is 
the  remnant  of  a  cavern  roof. 

136.  Springs.  —  Very  little  ground  water  remains  per- 
manently beneath  the  land  surface.  Sooner  or  later,  after 
descending  to  less  or  greater  depths,  it  returns  to  the  sur- 
face at  a  lower  level  than  where  it  entered,  coming  out  in 
the  form  of  springs  and  joining  the  run-off  of  streams. 

The  movement  of  ground  water  is  comparatively  slow 
while  percolating  among  the  particles  of  rock  waste  or 
through  the  pores  and  crevices  of  rocks.  Where  a  large 
part  of  the  rainfall  enters  the  ground,  the  volume  of  the 
streams  fed  by  springs  is  less  variable  than  where  the  rain- 
fall is  mostly  discharged  by  direct  run-off  during  and 
shortly  after  a  storm. 

It  is  for  this  reason  that  the  springs  and  streams  of  a 
forested  region  usually  have  a  comparatively  constant  flow ; 
but  this  rule  does  not  apply  in  regions  of  strong  relief,  such 
as  the  dissected  plateau  of  West  Virginia.  When  forests 
are  cut  down,  the  direct  run-off  of  the  rainfall  is  increased; 
then  the  springs  are  likely  to  run  dry  and  the  streams  will 
vary  greatly  in  volume  between  flood  and  drought. 

Ground  water  slowly  moves  from  hills  and  slopes, 
descending  to  lower  levels  and  accumulating  beneath  the 
lower  ground.  It  may,  therefore,  be  generally  found  near 
the  surface  in  valleys,  where  the  soil  is  usually  damp.     At 


RIVERS  AND  VALLEYS  237 

the  base  of  a  slope  the  ground  water  may  issue  in  a  spring, 
S,  Figure  119,  supplying  a  small  brook.  Innumerable 
small  springs  occur  unnoticed  in  the  banks  of  streams. 

Ground  water  stands  close  to  the  land  surface  in  marshes, 
swamps,  and  bogs,  rising  or  falling  somewhat  with  changes 
of  weather  and  season. 

In  regions  of  sufficient  rainfall  and  moderate  relief  the 
ground  water  may  be  reached  at  almost  any  point  except 
on  hilltops  by  sinking  wells  to  a  depth  of  from  ten  to  forty 


Fig.  119.    Section  showing  Ground  Water  in  Rock  Crevices  beneath  a  Valley 

feet.  The  bottom  of  the  well  should  be  a  few  feet  deeper 
than  the  level  at  which  the  trickling  stream  of  ground 
water  enters  it,  so  as  to  accumulate  water  in  sufficient 
volume  to  supply  ordinary  domestic  needs. 

Ground  water  and  spring  water  carry  very  little  rock 
waste  (unless  in  solution)  and  are  generally  clear  and  pure. 
For  this  reason  wells  and  springs  generally  afford  a  better 
water  supply  than  the  surface  streams  that  receive  the 
wash  of  fields  and  meadows. 

In  coastal  regions  groimd  water  may  flow  forth  as  springs 
directly  into  the  sea,  either  on  a  sloping  beach  near  low-tide 
level,  or  at  the  bottom  offshore;  here  they  sometimes  have 
a  current  so  abundant  as  to  supply  a  column  of  fresh  water 
that  ascends  through  the  heavier  salt  water  to  the  surface. 


238  ELEMENTARY  PHYSICAL  GEOGRAPHY 

137.    Artesian  Wells In   many  coastal   and   interior 

plains  a  large  part  of  the  rainfall  enters  the  more  sandy 
layers  and  follows  their  gentle  slope  deep  underground, 
between  other  layers  that  are  less  open  to  the  passage  of 
water.  If  a  deep  well  is  sunk  to  the  water-bearing  stratum, 
the  water  may  rise  and  flow  out  of  the  surface  like  a  foun- 
tain. Wells  of  this  kind  are  called  Artesian,  from  Artois, 
a  district  in  France  where  they  were  first  bored. 

It  is  essential  that  the  water-bearing  stratum  should 
receive  its  rainfall  at  a  higher  level  than  that  of  the  top 
of  the  well  by  which  it  is  tapped,  as  shown  in  Figure  120. 


Fig.  120.    Diagram  of  a  Coastal  Plain  with  Artesian  Wells 

In  what  part  of  the  plain  does  the  stratum  tapped  by  the  deeper 
well  reach  the  surface? 

Charleston,  Galveston,  and  many  other  coastal  cities 
receive  much  water  supply  from  artesian  wells.  In  east- 
ern Maryland  deep  wells  pierce  strata  that  reach  the 
surface  and  receive  rainfall  west  of  Chesapeake  bay;  the 
strata  lead  the  water  beneath  the  nearly  water-tight  layers 
that  floor  the  bay,  and  it  is  still  fresh  when  rising  in  the 
wells.  Southern  Wisconsin  and  eastern  Iowa  have  many 
artesian  wells,  supplied  by  water-bearing  strata  that  slope 
gently  away  from  the  older  land  of  northern  Wisconsin. 


RIVERS  AND  VALLEYS  289 

138.  Hot  and  Mineral  Springs.  —  Ground  water  some- 
times descends  deep  beneath  the  surface  with  a  slow  supply 
from  a  large  area.  While  deep  underground  the  water 
acquires  a  high  temperature  and  stands  under  a  heavy 
pressure.  It  is  shown  by  experiment  that  hot  water  under 
pressure  has  increased  power  of  dissolving  certain  minerals. 
Hence  the  slowly  percolating  water  takes  into  solution 
what  it  can  dissolve  of  the  more  soluble  minerals  dis- 
covered on  its  way,  such  as  calcite  (the  mineral  base  of 
limestone),  salt,  and  certain  compounds  of  magnesia,  iron, 
etc.  If  the  water  then  rises  rather  rapidly  along  a  rock 
fracture,  it  will  appear  at  the  surface  in  springs,  bearing 
an  unusual  amount  of  mineral  substances  in  solution  and 
often  having  a  high  temperature.  Such  springs  are  fre- 
quently of  medicinal  value. 

Springs  of  this  kind  are  associated  with  disturbed  rock 
structures  such  as  occur  in  mountainous  districts.  Saratoga 
Springs,  N.Y.,  White  Sulphur  Springs,  W.Va.,  Vichy  in 
central  France,  and  Karlsbad  in  Bohemia  are  examples  of 
settlements  determined  chiefly  or  wholly  by  the  value  of 
their  medicinal  waters.  Many  other  mineral  springs  occur 
in  the  Appalachian  and  Rocky  mountains. 

139.  Geysers.  —  In  certain  volcanic  regions  the  tempera- 
ture of  the  underground  water  may  rise  to  or  above  the 
boiling  point.  Steam  then  issues  with  the  water,  often  in 
a  more  or  less  explosive  manner,  and  such  steaming  and 
spouting  springs  are  called  geysers.  The  geysers  of  Ice- 
land have  long  been  famous ;  those  of  the  Yellowstone 
Park  are  now  the  most  celebrated  in  the  world. 


240 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


The  jet  of  steaming  water  and  spray  may  rise  for  several 
minutes  to  a  height  of  a  hundred  feet,  with  a  loud  roaring 
noise.  Then  all  remains  quiet  till  the  next  eruption, 
usually  a  number  of  hours  later.     Mineral  substances  that 

were  dissolved  in  small  quantity 
by  the  hot  water  underground 
are  partly  deposited  near  the 
geyser's  vent  as  the  water  cools 
or  evaporates,  and  thus  a  mound 
or  terrace  of  mineral  deposits  is 
gradually  formed.  The  terraces 
around  the  hot  springs  of  the 
Yellowstone  Park  are  of  great 
beauty. 

The  intermittent  action  of 
many  geysers  suggests  that  a 
certain  period  of  time  (an  hour 
or  more)  is  necessary  to  warm 
the  new  supply  of  water  that 
enters  the  crevice  of  discharge 
after  a  previous  supply  has  been 
blown  out  by  steam.  Water 
under  pressure  must  be  heated 
above  the  ordinary  boiling  point 
(212°  F.)  before  it  will  change  to  steam.  Hence  in  the 
deeper  part  of  the  crevice  the  temperature  of  the  boiling 
point  is  higher  than  at  the  surface.  When  the  deeper 
water  reaches  its  boiling  point  a  great  part  of  it  is  quickly 
converted  into  steam,  which  blows  the  rest  of  the  water  out 
of  the  vent. 


¥iQ.  121.    A  Geyser 


RIVERS  AND  VALLEYS  241 

140.  Mud  Volcanoes.  —  Certain  hot  springs  bring  a  con- 
siderable amount  of  fine  rock  waste  to  the  surface  with 
their  steaming  water.  The  waste  is  then  deposited  as  a 
muddy  sediment  around  the  opening  of  the  spring,  where 
it  forms  a  mound  with  a  hollow  or  crater  in  the  center. 
Although  seldom  over  a  few  score  feet  in  height,  the 
resemblance  of  these  mounds  to  true  volcanoes  has  given 
them  the  name  of  mud  volcanoes.  A  number  of  mud  .vol- 
canoes occur  in  the  Yellowstone. Park,  where  some  of  them 
are  only  a  few  feet  high.  Some  of  the  largest  known, 
with  heights  up  to  400  feet,  are  near  the  lower  course  of 
the  river  Indus  in  northwest  India. 

l(  141.  River  Systems  and  their  Parts.  —  A  river  is  a 
stream  of  water  bearing  the  rainfall  and  the  waste  of  the 
land  from  higher  to  lower  ground  and,  as  a  rule,  to  the  sea. 
A  trunk  stream  and  all  the  branches  that  join  it  constitute 
a  river  system. 

Stream  is  a  general  term,  with  little  relation  to  size. 
Rill,  rivulet,  brook,  and  creek  apply  to  streams  of  small 
or  moderate  size.  River  is  generally  applied  to  the  trunk 
or  to  the  larger  branches  of  a  river  system. 

A  river  flows  in  a  channel  that  is  somewhat  lower  than 
the  adjoining  land  surface.  The  floor  of  the  channel  is 
the  river  bed;  the  sides  of  the  channel  are  the  river 
banks.  The  coarser  part  of  the  waste  borne  by  the  liver 
is  swept  along  the  bed ;  the  finer  part  may  be  carried  in 
the  stream. 

The  land  from  which  a  river  gathers  its  water  and  its  load 
of  rock  waste  is  called  its  basin.  The  crest  line,  or  "height  of 


242 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


land,"  between  the  basins  of  neighboring  streams  or  rivers, 
or  between  the  valleys  of  river  branches,  is  called  a  divide. 


Fig.  122.    A  Dividing  Ridge  in  the  Mountains  of  Northwest  England 

Trace  the  divide  shown  in  Figure  122.  Note  that  a  divide  may 
be  much  higher  at  one  point  than  at  another.  Follow  some  of  the 
simple  and  branching  divides  shown  in  Figures  86  and  104. 


RIVERS  AND  VALLEYS  243 

The  land  slopes  in  opposite  directions  on  the  two  sides 
of  a  divide.  When  rain  falls  on  the  adjoining  slopes  it 
will  be  shed  into  different  streams;  hence  a  divide  is 
sometimes  called  a  watershed  or  water  parting.  Certain 
crest  lines  in  the  Rocky  mountains  separate  the  basins  of 
rivers  which  discharge  into  the  Atlantic  and  the  Pacific 
oceans;  these  crests  constitute  the  "continental  divide." 
Name  some  of  the  rivers  that  are  thus  divided. 

On  smooth  plains  and  uplands  there  is  no  well-marked 
height  of  land  or  ridge  separating  the  headwaters  and 
side  streams  of  neighboring  rivers.  Such  surfaces  may  be 
described  as  having  an  undivided  or  imperfectly  divided 
drainage.  Undivided  drainage  areas  are  often  found  on 
young  plains  and  plateaus.  Compare  the  foreground  and 
background  of  Figure  62  in  this  respect. 

When  a  plain  or  plateau  or  mountain  region  is  well 
dissected  numerous  sharply  defined  subdivides  are  devel- 
oped between  the  smaller  rivers  and  their  branches,  as 
on  the  Allegheny  plateau.  River  and  stream  basins  in 
vigorous  mountains  are  sharply  divided  by  the  crest  lines 
of  the  lofty  ridges  between  the  deeply  eroded  valleys.  A 
wojHi-down  region  may  have  indistinct  divides,  as  on 
the  even  uplands  of  the  Piedmont  belt  of  Virginia, 
Figure  99. 

Nearly  all  these  features  of  river  systems  may  be  illus- 
trated in  a  small  way  by  the  temporary  streams  on  a  road 
surface  just  after  a  fall  of  rain.  Many  interesting  studies 
may  be  made  of  the  small  stream  basins,  divides,  branches 
and  channels,  and  of  the  manner  in  which  the  streams 
bear  waste  from  higher  to  lower  ground. 


244  ELEMENTARY  PHYSICAL  G-EOGRAPHY 

142.  Floods  and  Droughts — The  volume  of  a  river  varies 
with  the  change  in  the  amount  of  rainfall  over  its  basin. 
During  and  shortly  after  a  rain  (or  a  thaw  of  snow)  the 
surface  run-off  is  most  active ;  all  the  rivulets  are  running 
with  water  and  waste  to  the  creeks,  and  the  creeks  run  to 
the  rivers.  The  volume  of  all  the  streams  is  increased  at 
such  a  time,  and  their  current  is  quickened.  The  water  is 
then  turbid  with  the  waste  that  has  been  washed  into  the 
streams  by  the  rivulets  on  the  valley  sides  and  lifted  from 
the  stream  beds  by  the  strengthened  currents.  As  the 
stream  volume  increases,  the  water  may  rise  above  the 
banks  of  the  channel  and  overflow  the  low  ground  or  flood 
plain  on  either  side.  There  some  of  the  fine  river-borne 
waste,  or  silt,  will  be  deposited  as  the  current  slackens. 

When  the  rain  stops  and  the  surface  run-off  lessens  and 
ceases  the  flooded  streams  are  drained  down  the  valleys 
toward  the  sea;  their  volume  decreases  and  their  surface  sinks 
to  a  more  ordinary  level.  Then  the  streams  must  depend  on 
ground  water  supplied  by  springs  at  innumerable  points  in 
the  stream  beds.  Less  waste  is  washed  into  the  streams  at 
this  time,  and  their  current  may  become  nearly  or  quite  clear. 

During  a  drought  of  several  weeks  or  months  the  streams 
drain  away  much  of  the  ground  water.  Then  the  discharge 
of  the  springs  is  weakened,  and  the  streams  are  reduced  to 
smaller  volume.  They  may  shrink  so  much  as  to  be  unable 
to  cover  all  the  bed  of  their  channel,  especially  in  the  head- 
water branches.  The  streams  may  entirely  disappear  for  a 
time,  but  even  if  lost  at  the  surface,  ground  water  may  gen- 
erally be  found  slowly  creeping  through  the  sand  and  gravel 
of  the  channel  bed  a  few  feet  below  the  surface. 


RIVERS  AND  VALLEYS  246 

In  regions  of  plentiful  rainfall,  like  the  eastern  United 
States,  the  rivers  may  be  much  reduced  during  droughts, 
but  they  do  not  entirely  disappear.  In  the  drier  climate 
of  many  of  the  Western  States  the  streams  habitually  dis- 
appear and  leave  their  channels  dry  during  the  long  inter- 
vals between  rain  storms. 

143.  The  Work  of  Rivers Frequent  reference   has 

already  been  made  to  the  work  of  rivers  in  sculpturing 
the  lands.  This  important  subject  may  now  be  con- 
sidered more  carefully.  The  higher  a  river  lies  above 
baselevel,  the  deeper  may  its  valley  in  time  be  worn. 
The  steeper  the  channel,  the  faster  the  river  flows  and 
the  more  and  the  coarser  rock  waste  it  may  sweep  and 
carry  downstream.  The  greater  the  volume  of  a  river  on 
a  given  slope,  the  less  it  is  retarded  by  friction  on  the  bed 
and  banks,  and  the  faster  it  flows.  Hence  a  river  in  flood 
flows  faster  than  at  time  of  low  water,  and  the  flooded 
current  transj)orts  a  greatly  increased  load  of  rock  waste. 
Indeed,  it  is  chiefly  in  time  of  flood  that  the  work  of  a 
river  is  performed. 

The  deepening  of  a  valley  by  the  erosion  of  rock  in  the 
river  channel  is  accomplished  chiefly  by  the  rasping  of  the 
rock  surface  with  the  innumerable  fragments  and  particles 
of  rock  waste  that  are  swept  »over  it.  The  more  resistant 
the  rock,  the  slower  it  will  be  worn  down.  The  particles 
thus  worn  from  the  rock  surface  make  part  of  the.  load  of 
waste  borne  away  by  the  river. 

As  the  valley  bottom  is  worn  deeper  and  deeper  below 
the  surrounding  country,  the  valley  sides  are  attacked  by 


246  ELEMENTARY  PHYSICAL  GEOGRAPHY 

the  weather,  and  much  Waste  washes  and  creeps  down 
from  them  into  the  river,  thus  widening  the  Valley, 
decreasing  the  steepness  of  its  side  slopes,  and  adding  to 
the  load  of  waste  borne  away  by  the  stream.  It  is  in  this 
sense  that  it  is  said  that  "rivers  erode  their  valleys." 
Another  portion  of  the  river  load  is  received  from  the 
headwaters  and  side  streams,  which  in  turn  receive  it 
chiefly  from  the  wash  of  waste  down  the  side  slopes  of 
their  valleys  at  times  of  rain  or  thaw. 

The  load  of  waste  thus  gathered  is  not  swept  along  in 
a  continuous  movement  to  the  sea ;  it  stops  many  times  on 
the  way,  being  laid  down  on  the  bed  or  sides  of  the  chan- 
nel when  the  water  is  low,  forming  bars  and  banks ;  it  is 
swept  forward  again  a  greater  or  less  distance  at  time  of 
flood. 

Rivers  that  are  beginning  their  work  of  erosion  and 
transportation  in  sculpturing  a  newly  uplifted  land  may  be 
called  young.  When  they  have  worked  so  long  that  all 
the  land  slopes  in  their  basin  have  been  worn  down  low, 
so  as  to  form  a  surface  of  faint  relief  —  a  peneplain  —  at 
a  small  altitude  above  sea  level,  the  rivers  may  be  called 
old.  Between  youth  and  old  age,  when  the  rivers  are 
actively  working  in  well-carved  valleys,  sweeping  along 
the  waste  received  from  the  hills  or  mountains  that  form 
the  valley  sides,  they  may  be  called  middle-aged  or  mature. 

144.  Young  Rivers.  —  The  examples  of  land  forms 
described  in  earlier  chapters  have  shown  that  when  a 
region  is  first  raised  from  the  sea,  or  when  a  former 
land  surface  is  uplifted,  tilted,  or  folded,  the  streams  as 


RIVERS  AND  VALLEYS  247 

a  rule  follow  the  lead  of  the  land  slopes,  uniting  here 
and  there  to  form  rivers  of  larger  and  larger  size. 

Young  rivers  thus  newly  established  proceed  to  cut 
down  their  channels  where  the  slope  is  steep  enough  to 
give  them  an  active  current;  the  waste  that  they  gather 
is  washed  along,  rasping  down  the  ledges  in  the  river 
bed;  but  where  the  slope  is  very  faint,  or  where  rivers 
enter  a  basin  holding  a  lake,  they  lay  down  their  load 
of  waste  and  build  up  the  land  surface. 

While  rivers  are  still  young  their  course  is  often 
marked  by  rapids  and  falls,  not  yet  eroded  away,  and 
by  lakes  not  yet  filled  up  with  sediments  or  drained 
away  by  the  deepening  of  their  outlet  by  the  outflowing 
stream.  The  cuiTcnt  of  such  rivers  is  irregular,  being 
very  fast  at  rapids  and  falls  and  almost  wanting  in  lakes. 
As  the  river  grows  older  both  the  falls  and  the  lakes  dis- 
appear and  the  current  becomes  more  uniform. 

The  drainage  of  the  Laurentian  highlands  of  Canada 
north  of  the  St.  Lawrence  river  bears  every  mark  of  youth. 
Lakes  are  very  numerous  and  of  irregular  form.  They 
often  have  several  outlets,  no  one  stream  having  cut 
down  enough  faster  than  the  others  to  secure  all  the 
discharge.  The  streams  are  frequently  interrupted  by 
rapids  or  falls  on  rock  ledges,  in  which  channels  are  as 
yet  cut  only  to  moderate  depth.  The  rivers  frequently 
split  into  two  or  more  channels,  which  reunite  after  wan- 
dering in  independent  courses  for  ten  or  twenty  miles 
across  country. 

These  highlands  are  a  rugged,  forested,  and  thinly  popu- 
lated wilderness  without  roads.     All  travel  is  by  canoes 


248 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


along  the  water  courses,  and  the  canoes  have  to  be  car- 
ried past  every  rapid  and  fall.  The  birch  tree,  from  whose 
bark  portable  canoes  are  made,  is  here  as  appropriate  to 
the  needs  of  the  inhabitants  as  the  camel  is  to  the  dwellers 
in  arid  deserts. 

The  St.  Lawrence  system,  with  its  many  lakes,  falls, 
and  rapids,  is  a  remarkable   example   of  very  young  or 


Fig.  123.    Niagara  Falls 


undeveloped  drainage.  The  outlet  of  Lake  Superior  is 
by  a  river  interrupted  by  rapids,  called  the  Sault  Sainte 
Marie  (Soo  St.  Mary).  The  outlet  of  Lake  Erie  is 
Niagara,  with  its  renowned  cataract  and  rapids.  The  out- 
let of  Lake  Ontario  is  the  St.  Lawrence,  with  numer- 
ous rapids.  The  lakes  favor  navigation,  but  the  rapids 
and  falls  obstruct  it.     Canals  and  locks  have  now  been 


RIVERS  AND  VALLEYS  249 

constructed,  by  which  the  rapids  and  falls  are  passed. 
Name  the  great  lakes  of  the  St.  Lawrence  system. 

The  region  of  the  great  African  lakes  bears  many  marks 
of  youthful  drainage.  The  lake  basins  here  indicate  a  break- 
ing or  warping  of  the  earth's  crust,  like  that  in  southern 
Oregon.  The  inclosing  plateaus  are  bordered  by  ragged 
cliffs,  where  fractures  have  taken  place.  The  Nile,  flowing 
north  from  Lake  Victoria  Nyanza,  and  the  Shire,  flowing 
south  from  Lake  Nyassa,  are  young  rivers  of  powerful  cur- 
rent, descending  over  falls  and  rapids,  and  are  very  busy  in 
the  work  of  deepening  their  valleys  and  draining  the  lakes. 

By  long-continued  action  the  path  of  a  river  will  in 
time  be  everywhere  worn  down  or  built  up  to  such  a 
slope  that  the  current  will  be  just  strong  enough  to 
carry  the  load  of  waste  that  it  receives.  Such  a  river 
may  be  described  as  passing  from  youth  to  maturity. 

145.  Lakes  may  be  generally  taken  to  indicate  a  youth- 
ful drainage  system,  as  in  the  examples  just  given.  In 
time  they  will  be  destroyed,  partly  by  filling  with  the 
waste  that  is  brought  by  the  inflowing  streams,  partly 
by  the  deepening  of  the  outlet  valley.  Lakes  should 
therefore  be  regarded  as  only  temporary  features  in  the 
long  life  of  the  river  system  to  which  they  belong.  The 
rivers  may  remain  long  after  the  lakes  disappear. 

The  depressions  between  the  tilted  lava  blocks  of  south- 
em  Oregon  hold  lakes  because  enough  time  has  not  yet 
passed  to  enable  the  streams  to  fill  and  drain  their  basins. 
Lava  flows  obstruct  streams  and  for  a  time  hold  back 
lakes.     Lakes  of  other  kinds  will  be  described  later. 


250  ELEMENTARY  PHYSICAL  GEOGRAPHY 

As  the  current  of  a  river  decreases  on  entering  a  lake, 
the  stream-borne  waste  settles ;  thus  deltas  are  formed  at 
the  inlets  and  the  lake  bottom  is  strewn  with  the  finest 
waste  or  silt. 

Lake  Geneva  in  Switzerland  receives  the  Rhone  at  its 
east  end ;  the  river  is  turbid  with  the  waste  that  it  has 
received  from  Alpine  glaciers  and  torrents.  A  delta 
twenty  miles  long  has  been  built  into  the  lake.  It  has 
grown  a  mile  forward  since  Roman  times,  nearly  2000 
years  ago.  The  lake  bottom  is  a  plain  of  fine  silt.  When 
even  the  finest  silt  has  settled,  the  lake  water  becomes 
very  clear,  and  the  Rhone  at  the  outlet  is  wonderfully 
transparent. 

Lakes  act  as  regulators  of  the  discharge  of  their 
outflowing  rivers ;  for  the  level  of  the  lake  changes 
little,  whether  the  inflowing  streams  are  flooded  or 
low,  and  hence  the  outlet  river  has  a  relatively  constant 
volume. 

The  Ohio  without  lakes  and  the  St.  Lawrence  with  five 
great  lakes  are  strongly  contrasted  in  respect  to  floods. 
The  latter  has  no  great  floods,  because  even  a  heavy 
rain  raises  the  surface  of  the  lakes  gradually  and  only 
by  a  small  amount;  hence  the  outflowing  river  cannot 
,be  greatly  increased  in  volume.  The  rains  of  the  upper 
Ohio  basin,  a  hilly  district,  are  not  detained  in  lakes,  but 
quickly  flow  down  the  hillsides  to  the  streams.  Floods 
in  the  Ohio  valley  may  rise  fifty  or  sixty  feet  in  a  few 
days,  spreading  to  ten  or  twenty  times  the  usual  width 
of  the  river  and  causing  great  damage  to  villages  and 
cities  on  the  valley  floor. 


RIVERS  AND  VALLEYS 


251 


146.  Falls  and  Rapids.  —  When  a  river  begins  to 
wear  its  valley  it  rushes  down  any  descending  slope 
that  occurs  on  its  course.  Here  a  gorge  is  cut  as  the 
rocks  are  rasped  away  by  the  gravel  and  sand  in  the 
rapid  current.  Niagara,  when  first  taking  its  present 
course,  fell   over  the   north-facing   bluff   of   the   upland 


rjTAR^<^ 


Fig.  124.    Diagram  of  Niagara  River  between  Lakes  Erie  and  Ontario 


that  separates  the  basin  of  Lake  Erie  from  that  of  Lake 
Ontario ;  since  then  the  river  has  cut  back  a  gorge  about 
seven  miles  long  from  the  edge  of  the  upland;  the  falls 
now  plunge  into  the  head  of  the  gorge.  The  larger  or 
Canadian  fall  is  now  retreating  three  or  more  feet  a  year 
at  its  middle. 

The  falls  of  the  Yellowstone  river  occur  at  the  head  of 
a  deep  canyon  cut  by  the  river  in  the  process  of  deepening 


252  ELEMEIS^TARY  PHYSICAL  GEOGRAPHY 

its  course  through  a  lava  plateau.     As  the  falls  are  worn 
back  the  gorge  is  lengthened. 

While  a  stream  is  engaged  in  deepening  its  valley  it 
often  flows  from  a  harder  to  a  softer  rock  structure.  It 
will  deepen  the  valley  muQh  more  quickly  in  the  latter 
than  in  the  former,  and  a  rapid  or  fall  will  be  formed  on 


Fig.  125.    Falls  of  the  Yellowstone  Kiver 

the  abrupt  slope  between  the  two.  Falls  and  rapids  of 
this  kind  are  numerous,  especially  in  dissected  plateaus 
and  mountains. 

It  has  long  been  the  custom  to  build  mills  near  falls,  so 
that  part  or  all  of  the  descending  water  may  be  used  to 
turn  water  wheels  and  thus  to  drive  the  machinery  of  the 
miUs.  Villages  have  often  grown  up  around  the  mills 
and  factories  thus  located.  -As  the  work  of  the  mills 
increases  it  has  frequently  been  necessary  to  add  steam 


RIVERS  AND  VALLEYS 


258 


power  to  water  power ;  at  the  same  time  the  village  may 
grow  to  be  a  large  city.  In  recent  years  it  has  been  found 
possible  to  transform  the  power  of  falling  water  into  an 
electric  current,  which  may  be  carried  many  miles  through 


Fig.  126.    Diagram  of  Torrent,  with  Falls  and  Reaches 

How  many  falls  are  shown  in  Figure  126?  Draw  a  profile  along 
the  river  course  and  compare  its  slope  at  and  between  the  falls. 
Why  are  some  of  the  stretches  between  the  falls  longer  than  others  ? 
Where  are  the  gorges  deepest  ? 

wires  and  then  set  to  work  to  drive  machinery,  to  run 
cars,  or  to  furnish  electric  light.  Waterfalls  in  thinly 
populated  mountains  may  thus  in  time  come  to  be  used  to 
supply  electric  power  to  cities  on  the  neighboring  plains. 


254  ELEMENTARY  PHYSICAL  GEOGRAPHY 

147.  Graded  Rivers.  —  A  river  cannot  wear  down  its 
course  to  a  level,  for  there  must  be  some  slope  down 
which  the  current,  bearing  its  load  of  rock  waste,  may- 
flow  toward  its  mouth.  While  the  slope  is  strong  and 
the  current  is  very  swift  the  stream  is  called  a  torrent. 
The  waste  is  then  swept  along  so  actively  that  bare  rock 
is  commonly  seen  in  the  stream  bed.  Torrential  streams 
are  usually  clear,  because  they  quickly  sweep  away  the 
fine  particles  that  they  receive  from  time  to  time,  leaving 
coarse  cobbles  and  bowlders  lying  on  their  rocky  channels. 
Such  streams  are  still  young. 

As  time  passes  and  the  channel  is  eroded  deeper  and 
deeper  it  will  be  worn  down  more  nearly  level,  closer  arid 
closer  to  baselevel.  But  it  must  always  preserve  a  slope 
sufficient  to  give  the  water  a  velocity  that  will  enable  it 
to  wash  forward  the  load  of  waste  received  from  the  head- 
waters and  side  streams,  though  without  either  deepening 
or  building  up  the  bed  of  the  channel  significantly.  When 
such  a  slope  is  attained  the  river  is  said  to  be  graded.  It 
has  reached  maturity. 

The  current  of  a  graded  river  is  usually  deliberate 
instead  of  torrential.  Its  bed  and  banks  consist,  for  the 
most  part,  of  deposits  of  rock  waste ;  firm  ledges  are  seldom 
seen  along  its  course.  The  water  is  usually  made  some- 
what turbid  or  muddy  by  the  presence  of  fine  waste,  with 
which  it  is  plentifully  supplied  by  its  tributaries  and  by 
the  wash  from  its  bed  and  banks. 

In  valleys  among  high  mountains,  where  an  abundant 
supply  of  coai-se  waste  is  washed  down  from  the  steep 
valley  sides,  graded  streams  must  have  a  slope   strong 


RIVERS  AND  VALLEYS  265 

enough  to  give  them  an  active  current ;  otherwise  their 
coarse  and  abundant  load  cx)uld  not  be  washed  forward. 
In  lowlands  where  only  fine-textured  waste  of  the  land  is 
slowly  washed  into  the  streams,  graded  rivei*s  have  a  very 
gentle  descent. 

Water  moves  so  easily  that  large  rivers  assume  very 
faint  slopes;  the  lower  Mississippi  has  a  descent  of  only 
two  or  three  inches  to  the  mile,  yet  it  bears  along  a  vast 
amount  of  rock  waste,  —  6700  million  cubic  feet  of  sus- 
pended silt,  750  million  of  silt  dragged  along  the  bottom, 
and  1400  million  of  minerals  in  solution  every  year. 

148.  Reaches  and  Rapids.  —  A  longer  time  is  required 
to  wear  a  valley  down  to  grade  where  the  rocks  are  resist- 
ant than  where  they  are  weak.  If  a  river  crosses  a  suc- 
cession of  weak  and  strong  rocks,  as  in  Figure  126,  the 
graded  condition  will  be  first  attained  on  the  weak  rocks, 
and  each  reach  of  the  river  on  the  weak  rocks  will  be 
graded  with  reference  to  the  sill  of  hard  rocks  next  down- 
stream or  with  reference  to  the  lake  or  sea  into  which  the 
river  may  flow.  The  sills  of  hard  rocks  then  serve  as  local 
baselevels  with  respect  to  which  the  stretch  or  reach  next 
upstream  is  graded. 

Many  rivers  come  in  this  way  to  be  divided  into  long 
smooth  reaches  and  short  plunging  rapids  or  falls.  Most 
of  the  rivers  of  New  England  and  of  eastern  Canada  are 
in  this  condition. 

When  a  river  system  has  been  undisturbed  for  a  long 
period  of  time,  even  the  resistant  rocks  are  worn  down. 
Few  falls  then  remain  to  interrupt  the  steady  flow  of  the 


256  ELEMENTARY  PHYSICAL  GEOGRAPHY 

river  current,  and  its  graded  reaches  become  longer  and 
longer.  The  side  streams,  following  the  example  of  the 
master  stream,  wear  down  the  side  valleys  so  as  to  join  the 
main  valley  at  even  grade.  It  is  in  this  well-established 
condition  that  many  large  rivers  of  the  world  are  found. 
When  a  graded  condition  is  reached  in  even  the  smaller 
branches  of  a  river  system  the  slope  will  be  steepest  in 
the  headwater  streams  and  least  near  the  river  mouth; 
thus  the  profile  of  a  well-developed  river  is  a  curve  of 
decreasing  slope  from  head  to  mouth. 

149.  The  Development  of  Valleys.  —  While  a  young  river 
is  deepening  its  valley,  the  valley  sides  are  steep  and  the 
valley  bottom  is  no  wider  than  the  river  channel,  as  in  Fig- 
ure 127.  At  such  a  time  the  valley  floor  offers  no  attraction 
to  settlement,  as  it  affords  no  level  ground  for  roads  near 
the  river ;  roads  built  in  such  a  valley  must  perch  on  the 
side  slope.  If  the  valley  is  deep,  like  the  Colorado  canyon, 
it  may  act  as  a  barrier  between  the  uplands  on  either  side. 

Floods  have  little  room  to  spread  in  a  steep-sided  valley ; 
hence  they  rise  rapidly  on  the  valley  walls,  even  thirty 
feet  or  more  in  a  day  or  two.  Thus  confined  in  the  valley, 
the  flood  flows  rapidly  and  sweeps  away  all  obstacles, 
gradually  subsiding  as  its  supply  of  water  lessens. 

It  is  for  this  reason  difficult  to  maintain  road  bridges 
across  the  streams  of  the  Allegheny  plateau.  Figure  79; 
the  great  expense  of  building  strong  and  high  bridges  can- 
not be  borne  by  the  scattered  population.  The  streams 
are  therefore  commonly  crossed  by  fording.  At  time  of 
high  water  travel  is  interrupted. 


RIVERS  AND  VALLEYS 


257 


The  continued  action  of  the  river,  wearing  first  on 
one  bank  and  then  on  the  other,  gradually  widens  the 
valley  floor.     At  the  same  time  the  sides  of  the  valley  are 


Fig.  127.    Valley  of  Yakima  River,  Washington 

worn  back  to  gentler  slopes,  and  the  valley  floor  becomes 
more  accessible. 

At  this  stage  of  development  the  valley  is  much  more 
available  for  human  uses  than  when  young,  narrow,  and 


258  ELEMENTARY  PHYSICAL  GEOGRAPHY 

steep-walled.  Villages  may  be  built  and  fields  may  be 
cultivated  on  the  valley  floor.  Roads  may  follow  it  on 
each  side  of  the  river.  Instead  of  being  a  trenchlike  bar- 
rier between  two  highlands,  the  valley  has  now  become  a 
well-graded  pathway  for  settlement  and  for  trade  between 
the  upper  and  lower  parts  of  the  river  system  to  which  it 


Fig.  128.    The  Mohawk  Valley 

belongs.  The  Mohawk  valley  in  eastern  New  York,  Fig- 
ure 128,  is  a  good  example  of  this  kind.  Another  is 
shown  in  Plate  X. 

The  behavior  of  rivers  during  the  advance  in  the  devel- 
opment of  their  valleys  must  now  be  considered  in  greater 
detail. 

150.  The  Development  of  Flood  Plains.  —  In  a  winding 
stream  the  fastest  current  is  displaced  from  the  middle 
of  the  channel  toward  the  outer  bank.      Such  a  stream 


1^ 


RIVERS  AND  VALLEYS 


259 


therefore  tends  to  cut  more  on  the  outer  bank  than  on 
the  inner  bank  at  every  turn;  hence  as  it  cuts  down  it 
also  cuts  sideways. 

When  grade  is  reached  the  valley  walls  will  be  slant- 
ing, but  they  will  be  steepest  on  the  outer  side  of  every 
bend,  where  the  stream  has  undercut  the  valley  wall,  as  in 
Figure  129.  The  valley  walls  will  therefore  be  equally 
steep  on  the  two  sides  only  where  the  valley  is  straight. 
At  each  turn  sloping  spui's  descend  opposite  abrupt  cliffs, 
and  the  belt  of  country  occu- 
pied by  the  turns  of  the  river 
is  broader  than  at  first. 

Draw  a  map  of  the  district  shown 
in  Figure  130  a,  following  the  style 
of  Figure  129,  and  show  where  the 
river  is  undercutting  the  cliffs. 
The  river  is  supposed  to  be  flowing 
toward  the  front  of  the  diagram 
in  Figure  130. 

Fig.  129.    Outline  Map  of  a 

When  a  river  has  worn  down  Young  Valley 

its  valley  to  a  gentle  slope  it 

still  wears  on  the  outer  bank  of  every  turn,  because  the 
strong  current  runs  there ;  thus  the  valley  floor  is  broad- 
ened. At  the  same  time  the  turns  tend  to  become  smooth 
curves  of  regular  form. 

As  the  outer  bank  of  a  curving  channel  is  slowly  cut  away, 
the  inner  bank,  where  the  current  runs  slower,  is  gradually 
filled  up  nearly  to  high-water  level  with  rock  waste  from 
farther  upstream.  A  curved  strip  of  flat  valley  floor  is 
thus  developed  on  the   inner  side  of  each  curve,  as  in 


260 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Figure  1305,  first  on  one  side  and  then  on  the  other  side  of  the 

rivjer.  As  the  valley  floor 
is  exposed  to  overflow  at 
times  of  flood,  the  flat 
land  bordering  the  stream 
is  called  the  flood  plain. 

Draw  a  map  of  the  district 
in  Figure  1305.  Describe  the 
shape  and  position  of  the 
patches  of  flood  plain.  What 
difficulties  would  be  met  in 
making  a  road  along  the  val- 
ley bottom  ? 

With  continued  action 
the  river  consumes  more 
and  more  of  the  spurs  that 
enter  its  curved  course,  as 
in  Figure  130  c,  c?.  In 
time  the  spurs  are  all  worn 
away,  as  in  Figure  130  e. 
Then  an  open  flood  plain 
is  formed  on  which  the 
river  freely  follows  such  a 
curved  course- as  best  suits 
its  volume.  With  still  fur- 
ther action  of  the  river  the 
flood  plain  will  be  slowly 
Fig.  130.   Diagrams  of  a  Widening  Valley  ^idenedto  greater  breadth. 

The  valley  will  then  be  more  attractive  to  settlement  than 
before,  with  room  for  villages  and  fields  on  its  floor. 


RIVERS  AND  VALLEYS  261 

Which  side  (up-valley  or  down-valley)  of  the  middle  spur  in 
Figure  130  c  has  been  worn  away?  Draw  a  map  representing 
Figure  130  d. 

Describe  the  form  of  the  upland  in  the  diagrams  of  Figure  130. 
Compare  the  form  and  breadth  of  the  flood  plain  in  the  different 
diagrams.  Compare  the  slopes  of  the  valley  sides.  Compare  the 
forms  of  the  upland  spurs  that  enter  the  curves  of  the  valley. 

When  a  river  overflows,  the  greatest  amount  of  silt 
is  laid  down  on  the  flood  plain  near  the  river  channel. 
Thus  in  time  the  plain  comes  to  have  a  gentle  slope 
away  from  the  river  on  either  side,  as  well  as  down  the 
valley. 

If  a  stream  has  a  large  load  of  coarse  rock  waste,  its 
graded  flood  plain  must  be  relatively  steep  (a  descent  of 
from  five  to  twenty  feet  or  more  in  a  mile).  In  this  case 
the  stream  does  not  turn  far  aside  from  a  direct  course 
along  the  flood  plain  to  form  serpentine  curves;  but  it 
is  constantly  embarrassed  by  the  formation  of  bars  and 
islands  of  gravel  and  sand,  splitting  its  current  into  a 
braided  network  of  channels. 

The  Platte  is  a  river  of  this  kind.  It  gathers  much 
waste  from  the  weaker  rocks  of  the  Great  plains  and 
therefore  requires  a  rather  strong  slope  for  its  graded 
valley  floor.  Many  rivers  flowing  from  the  Alps  to  the 
lower  lands  have  gravel  bars  and  islands  between  their 
braided  channels,  as  in  Plate  XI. 

151.  River  Meanders.  —  If  the  waste  borne  by  a  river 
is  of  very  fine  texture,  the  flood  plain  will  have  a  veiy 
gentle  grade.  Then  the  river  easily  turns  aside  from  a 
direct  course  on   its  broadened  flood  plain,  and  in  this 


262 


ELEMEI^TTARY  PHYSICAL  GEOGRAPHY 


way  (whatever  its  original  path)  develops  a  system  of 
serpentine  curves,  as  in  Figure  130  c?,  e.  Curves  of  this 
kind  are  called  meanders,  after  the  Meander,  a  winding 
river  of  Asia  Minor.  How  many  turns  does  the  river 
make  in  Figure  131? 

The  size  of  the  meanders  increases  with  the  volume  of 
the  stream.     A  meadow  brook  may  swing  around  curves 


Fig.  131.    A  Meandering  River,  Vale  of  Kashmir,  India 

measuring  only  forty  or  fifty  feet  across.  The  curves  of 
the  lower  Mississippi  are  from  three  to  six  miles  across. 
The  flatter  the  flood  plain,  the  greater  is  the  meander  turn- 
ing. The  Koros,  Figure  132,  on  the  Plain  of  Hungary, 
has  its  meanders  remarkably  developed. 

Meanders  are  slowly  changed*,  for  the  river  wears  away 
the  outer  bank  of  each  curve  because  the  current  runs 
fastest  there;  the  opposite  side  of  the  channel  is  filled 


RIVERS  AND  VALLEYS 


268 


in  with  waste  where  the  current  is  slow.  The  Mississippi 
below  Cairo  has  in  the  course  of  ages  shifted  its  coursie, 
now  eastward,  now  westward,  and  has  thus  opened  a  flood 
plain  from  twenty  to 'sixty  miles  wide,  that  is,  five  or  six 
times  wider  than  its  meander  belt.  Similar  changes  may 
be  seen  on  a  small  scale  in  a  meadow  brook. 

In  the  fine  silt  of  a  broad  and  flat  flood  plain  a  large  river 
changes  its  course  easily  and  rapidly;  it  takes  material 
from  the  outer  bank, 
where  its  current  is 
strong,  and  deposits  it 
farther  downstream 
on  the  inner  bank, 
where  the  current  is 
weaker. 

The  necks  of  the 
flood-plain  spurs  be- 
tween adjoining 
meanders  are  often 
gradually    narrowed 

and  cut  through  by  the  river,  the  meander  around  the 
spur  being  then  deserted  for  a  shorter  and  more  direct 
course,  called  a  cut-off.  Where  are  cut-offs  likely  to 
occur  in  Figure  132? 

Large  rivers,  like  the  Mississippi,  exhibit  all  stages 
of  this  process.  An  abandoned  meander  is  occupied 
by  nearly  stagnant  water,  more  or  less  completely  sep- 
arated from  the  new  and  shorter  channel  by  deposits 
of  silt  in  the  ends  of  its  arms;  in  time  it  becomes  an 
oxbow  lake. 


Fig.  132.    A  Meandering  River  on  the 
Plain  of  Hungary 


264 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Draw  an  outline  map  to  show  the  probable  path  of  the  Mississippi 
when  it  ran  through  the  oxbow  lakes,  Figure  133.  How  does  the 
channel  of  1896  differ  from  that  of  1882  ? 

The  shifting  of  the  channel  may  be  checked  by  pro- 
tecting the  outer  bank 


with  stone  or  wood, 
but  this  is  expensive. 
Rising  floods  may  be 
held  back  by  dikes  or 
levees  built  on  the 
plain  a  little  distance 
from  the  river  banks. 
When  the  levees  are 
overtopped  or  breached 
widespread  floods  may 
result,  such  as  occurred 
on  the  Mississippi  flood 
plain  in  April,  1897, 
when  about  13,000 
square  miles  of  the 
plain  (two  fifths  of  the 
entire  area)  were  under 

Meandering   Channel  and   Oxbow  water.      The   valuc    of 
Lakes  in  the  Flood  Plain  of  the  Mississippi,  ,  , 

according  to  Surveys  in  1882  and  1883.    The  ll^®    StOCK    and    CropS 

position  of  the  channel  according  to  surveys  lost  in   this   flood  WaS 


Fig.  133. 


in  1895  and  1896  is  shown  by  dotted  lines. 


estimated  at  |15,000,- 


000 ;  many  thousands  of  people  were  for  a  time  driven 
from  their  homes. 

In  March,  1890,  a  strong  flood  in  the  lower  Mississippi 
broke  through  the  levees  on  the  left  bank,  forming  the 


RIVERS  AND  VALLEYS  265 

"  Nita  crevasse  "  (a  break  on  the  Nita  plantation),  flood- 
ing the  plain,  carrying  river  silt  into  the  shallow  waters  of 
the  Gulf  of  Mexico,  and  ruining  the  oyster  beds  east  of 
the  delta. 

152.  Alluvial  Fans  of  Large  Rivers. — When  rivers  flow 
from  mountains  or  plateaus  and  enter  open  lowlands, 
where  no  valley  walls  inclose  them,  they  may  build  exten- 
sive alluvial  fans  of  faint  slope.  The  Merced  river  of 
California  (see  Jf,  Figure  134)  offers  a  good  illustration 
of  this  habit. 

The  Merced  gathers  much  waste  from  its  steep  head- 
waters in  the  Sierra  Nevada.  On  issuing  from  its  narrow 
valley  at  the  mountain  base  it  is  free  to  run  in  any  direc- 
tion —  forward,  to  the  right  or  to  the  left  —  on  the  Jbroad 
"  valley  of  California,"  a  belt  of  low  country  between  the 
Sierra  and  the  Coast  range.  Here  the  river,  flowing  first 
in  one  direction,  then  in  another,  has  built  a  fan  about 
forty  miles  in  radius,  of  gravel  near  the  mountains,  of  fine 
silt  farther  forward. 

As  the  rain  of  this  region  falls  chiefly  in  winter,  it  is 
necessary  to  irrigate  the  fields  for  summer  crops.  Nothing 
could  be  better  adapted  to  the  needs  of  irrigation  than  a 
gently  sloping  alluvial  fan;  for  the  river  may  be  easily 
turned  into  various  channels  at  the  head  of  the  fan  and 
led  forward  on  different  courses,  and  thus  distributed  over 
thousands  of  acres. 

One  of  the  largest  alluvial  fans  in  the  world  is  that  of 
the  Hoang-Ho,  in  eastern  China.  This  great  river,  bear- 
ing a  heavy  load  of  fine  silt  from  the  basins  among  the 


266 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


inner  mountains,  issues  from  its  inclosed  valley  300  miles 
inland  from  the  present  shore  line,  and  at  a  height  of  about 
400  feet  above  sea  level,  and  then  flows  to  the  sea  down 
the  gentle  slope  of  its  extensive  fan. 

The  great  fan  of  the  Hoang-Ho 
is  very  fertile  and  supports  one 
of  the  densest  populations  on  the 
earth ;  but  it  is  subject  to  overflow 
on  a  vast  scale,  when  the  river 
suddenly  changes  its  course  from 
one  path  to  another  and  invades 
fields  and  villages  on  a  new  course 
to  the  sea.  Overflow  is  prevented 
as  far  as  possible  by  dikes;  but 
the  channel  has  repeatedly  been 
changed  during  the  many  cen- 
turies of  Chinese  history. 

The  loss  of  life  caused  by  these 
overflows  is  very  great.  Not  only 
are  many  thousands  of  people 
drowned,  but  the  crops  are  de- 
stroyed over  large  districts,  caus- 
ing famines  in  which  many  more 
thousands  perish. 


Fig.  134.    The  Valley  of 
California 


153.  Broad  Plains  formed  by  Rivers.  —  When  many 
rivers  flow  forth  from  mountain  valleys  upon  a  neighboring 
lowland  their  adjoining  fans  unite  in  a  broad  plain  slop- 
ing gently  forward  from  the  mountain  base.  This  may  be 
called  a  river-made  plain.     It  resembles  a  coastal  plain  in 


RIVERS  AND  VALLEYS 


267 


having  higher  land  for  a  background,  but  it  does  not  neces- 
sarily front  upon  the  sea,  and  it  is  generally  but  little 
trenched  by  the  rivers  that  built  it.  A  plain  of  this  kind 
often  occupies  the  depression  between  two  highlands  or 
mountain  ranges. 

The  many  rivers  issuing  from  the  valleys  of  the  Sierra 
Nevada  and  the 
Coast  range  upon 
the  "valley  of  Cali- 
fornia" have  formed 
an  extensive  plain, 
of  which  the  Mer- 
ced fan,  described 
above,  is  only  a  part. 
The  successive  fans 
are  veiy  broad  and 
flat,  so  that  their 
slightly  convex  form 
can  hardly  be  seen. 
The  fans  from  the 
east  and  Avest  meet 
in  a  flat-floored 
trough,  Figure  134. 


Fig.  i:i5.    Torrent  Fan  Delta,  Lake  Geneva, 
Switzerland 


154.  Deltas.  — AVhen  a  river  enters  a  lake  or  the  sea  its 
current  is  checked.  The  finest  part  of  the  waste  may  be 
swept  away  by  waves  and  tides ;  the  rest  accumulates  at 
the  river  mouth  and  builds  up  a  new  land  surface,  called  a 
delta.,  in  advance  of  the  original  shore  line.  The  fans  of 
mountain  torrents  form  deltas  in  lakes  at  the  mountain 


268 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


NORTHPASS 


SOUTHEAST 
PASS 


base.  Small  deltas  are  characteristic  of  young  rivers ;  the 
longer  the  progress  of  river  growth,  the  larger  the  delta 
may  become. 

The  land  surface  of  a  delta  is  built  on  the  same  slope 
as  that  of  the  river  flood  plain  farther  upstream,  the  delta 
being  only  the  forward  part  of  the  flood  plain.  Under 
water  a  delta  slopes  at  a  steeper  angle  than  above  water. 

The  great  fan  of 
the  Hoang-Ho  may  be 
regarded  as  its  delta, 
because  it  has  been 
built  forward  into  the 
Yellow  sea  (so  named 
from  the  color  given 
by  the  river  waste). 

A  river  frequently 
splits  into  several 
channels  on  its  delta, 
the  outgoing  branches 

F,G.136.    The  Delta  o£  the  Mississippi  j^^j^^   j^^^^   ^    ^^_ 

tributaries.  These  are  well  exhibited  in  the  fingerlike 
divisions  of  the  Mississippi  on  its  outer  delta.  Figure  136, 
and  in  the  many  channels  of  the  Ganges  and  the  Brahma- 
putra on  their  deltas  at  the  head  of  the  Bay  of  Bengal. 
How  many  distributaries  are  shown  in  Figure  136  ? 

Great  rivers  may  build  their  deltas  in  the  face  of  waves 
and  tides.  At  the  Mackenzie  delta  the  tidal  range  is  three 
feet,  at  the  Niger  four  feet,  at  the  Hoang-Ho  eight  feet, 
at  the  Ganges-Brahmaputra  eighteen  feet.  The  building 
of  deltas  by  small  rivers  is  favored  by  the  protection  from 


SOUTBPASS 


&  SOUTHWEST  PASS 


RIVERS  AND  VALLEYS  269 

waves  in  bay  heads  and  by  the  weakness  or  absence  of 
tides.     Where  are  the  alx)ve-named  rivers  ? 

The  absence  of  deltas  at  the  embayed  mouths  of  certain 
rivers  is  frequently  not  so  much  because  the  tidal  currents 
sweep  away  all  the  river  silt,  as  because  there  has  not  yet 
been  time  enough  to  build  a  delta  since  the  embayments 
were  formed  by  the  depression  of  the  coastal  lands. 

The  lower  valleys  of  the  Delaware,  Susquehanna,  Poto- 
mac and  neighboring  rivers  are  drowned,  forming  bays  in 
the  partly  submerged  coastal  plain  of  the  Middle  Atlantic 
States.  Whatever  deltas  these  rivei-s  previously  built  are 
now  beneath  the  sea.  Very  little  delta  growth  has  yet 
taken  place  at  the  bay  heads ;  hence  the  depression  of  the 
region  is  relatively  recent. 

The  deltas  of  large  rivers  consist  of  fine-textured  waste 
or  silt,  worn  during  the  long  journey  from  the  river  head- 
waters and  weathered  during  many  rests  in  the  flood  plain 
on  the  way.  In  a  favorable  climate  deltas  are  very  fertile 
and  attract  a  large  population.  The  three  densest  popula- 
tions of  the  world  (outside  of  large  cities)  are  in  eastern 
China,  northeastern  India,  and  northern  Italy,  all  on  the 
lower  flood  plains  and  deltas  of  large  rivers. 

155.  Mature  Rivers.  —  When  a  river  and  its  larger 
branches  have  destroyed  their  lakes  and  falls  and  reduced 
their  valleys  to  graded  slopes,  when  all  the  side  valleys 
join  the  larger  valleys  at  grade,  w:hen  the  larger  streams 
have  broadened  their  valley  floors  so  that  they  can  meander 
freely  upon  flood  plains  in  curves  appropriate  to  their 
volume,  and  when  a  delta  is  built  forward  at  the  river 


270  ELEMENTARY  PHYSICAL  GEOGRAPHY 

mouth,  the  river  system  has  reached  the  mature  or  full- 
grown  stage  of  its  development. 

Mature  rivers  accomplish  the  drainage  of  their  basins 
and  the  carrying  of  rock  waste  to  the  sea  in  the  most  per- 
fect manner.  No  undivided  uplands  remain  from  which  a 
great  part  of  the  rainfall  may  be  returned  to  the  atmos- 
phere by  evaporation.  The  largest  possible  share  of  the 
rainfall  is  shed  from  the  well-carved  surface  of  the  land 
and  runs  off  in  the  streams  with  no  delay  in  lakes  or  haste 
in  falls.  No  hard  rock  ledges  remain  to  be  worn  down  in 
the  valley  floors.  Everywhere  the  waste  of  the  land  is 
washed  down  the  slopes  to  the  streams  and  delivered  in 
such  quantity  that  the  streams  are  kept  working  at  their 
full  capacity  to  transport  the  waste  toward  the  sea. 

The  valleys  of  mature  rivers  are  easily  followed  by  roads 
and  railroads ;  they  are  broad  enough  to  contain  cultivated 
fields  as  well  as  villages  and  cities,  as  in  Plate  X. 

156.  Old  Rivers.  —  If  no  disturbance  occurs,  a  maturely 
developed  river  system  passes  by  slow  degrees  into  a  quiet 
old  age.  The  hills  waste  away  to  fainter  slopes  and  yield 
less  and  less  waste  to  the  streams.  The  texture  of  the 
waste  becomes  finer  and  finer.  More  of  the  waste  is  car- 
ried in  solution. 

The  extreme  old  age  of  a  river  system  would  be  char- 
acterized by  low  and  ill-defined  divides  between  faint  slopes 
leading  to  broad  flood  plains,  on  which  the  streams  would 
meander  with  great  freedom.  An  increasing  share  of  the 
transported  waste  would  be  dissolved.  A  large  amount  of 
rainfall  might  be  lost  by  evaporation  on  the  gentle  slopes. 


RIVERS  AND  VALLEYS  271 

It  is  unusual  to  find  an  old  river  system.  The  lower 
trunks  of  large  river  systems  often  gain  very  gentle  slopes 
and  free-swinging  meanders,  but  before  old  age  is  attained 
by  all  the  small  side  branches  and  the  headwaters  move- 
ments of  elevation  or  depression  generally  occur  in  the 
earth's  crust,  with  more  or  less  tilting  and  breaking;  and 
in  this  way  the  rivers  are  made  young  again  and  set  to 
work  at  new  tasks. 

157.  Revived  Rivers.  —  At  any  stage  in  the  erosion  of 
a  region  drained  by  a  river,  the  river  basin  may  be  uplifted 
to  a  greater  height  above  sea  level.  Then  the  river  will 
at  once  begin  to  cut  its  valley  floor  deeper  than  it  could 
have  done  before.     Such  rivers  may  be  called  revived. 

Old  rivers  flowing  across  low  worn-down  mountains  are 
rare,  but  revived  rivers  flowing  through  gorges  in  uplifted 
lowlands  of  this  kind  are  common.  The  rivers  and  their 
narrow  valleys  in  the  Piedmont  district  of  Virginia  are 
thus  explained. 

If  a  meandering  river  is  revived,  it  will  intrench  itself 
beneath  its  former  flood  plain ;  then  its  new  valley  will  be 
regularly  curved  after  the  pattern  of  its  meanders. 

The  north  branch  of  the  Susquehanna  follows  a  deep 
and  winding  valley  of  this  kind  through  the  Allegheny 
plateau  of  northern  Pennsylvania.  The  Osage  has  an 
extremely  serpentine  valley  in  the  uplands  of  central  Mis- 
souri. Both  these  rivers  seem  to  have  learned  to  meander 
when  the  uplands  were  lowlands.  Since  these  regions 
were  raised  the  rivers  have  cut  down  valleys  of  a  meander- 
ing pattern.     The  valleys  are  still  narrow.     The  rivers  are 


272 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


enlarging  their  curves  by  cutting  away  the  outer  bank; 
here  the  river  is  bordered  by  steep  bluffs.  Strips  of  flood 
plain  are  beginning  to  form  on  the  inside  of  the  river 

curves  where  the    banks 
are  low  and  flat. 


Fig.  137.    Diagram  of  a  Narrowed  Spur 
in  a  Meandering  Valley 


Draw  a  map  of  the  district 
shown  in  Figure  137.  Describe 
the  form  and  arrangement  of 
the  patches  of  flood  plain. 
Where  are  the  valley  sides 
steep  ?  Where  are  their  slopes 
gentler  ? 


It  sometimes  happens  that  a  revived  meandering  river, 
eroding  its  outer  bank,  may  wear  through  the  neck  of  the 
narrowest  upland  spurs  that  enter  its  trenched  course ;  it 
will  then  desert  a  round- 
about course  for  a  more  ^ 
direct  one,  Figures  137, 
138.  Rapids  will  occur  |, 
for  a  time  at  the  cut-off. 

Draw  two  maps  of  the  dis- 
trict shown  in  Figure  138,  one 
showing  the  path  of  the  river    Fig.  138.    Diagram  of  Cut-Off  Spur  in  a 
just    before    the    cut-off    was  Meandering  Valley 

made,    one    just    afterwards. 
Compare  the  first  of  these  maps  with  the  one  drawn  from  Figure  137. 

The  village  of  Lauffen  (Rapids)  on  the  river  Neckar  in 
southern  Germany  gains  water  power  from  rapids  formed 
at  a  recent  cut-off.  The  former  course  of  the  river  is  seen 
in  a  meadow  beautifully  curved  around  an  isolated  hill, 


RIVERS  AND  VALLEYS 


273 


the  cutoff  end  of  an  upland  spur,  Figure  139. 
cut-off  spur  is  seen  near  the  village  of  Hofen. 


Another 


158.  Water  Gaps. — Many  rivers  cross  the  hard-rock 
ridges  of  the  Allegheny 
mountains  of  Pennsyl- 
vania in  sharp  notches, 
called  water  gaps.  For 
example,  the  Delaware 
river  gathers  many 
branches  from  the  open 
valleys  of  northeastern 
Pennsylvania  and  es- 
capes by  a  deep,  narrow 
notch,  called  the  Dela- 
ware water  gap,  in  Kitta- 
tinny  mountain,  at  the 
northwestern  corner  of 
New  Jersey. 

Such  cases  are  ex- 
plained as  follows.  Once 
the  whole  region  stood 
lower  than  now  and  a 
lowland  spread  far  and 
wide  at  about  the  level  of  what  are  the  ridge  crests  to-day. 

With  the  elevation  of  the  region  all  the  revived  rivers 
begin  to  wear  down  their  valleys.  Where  a  trunk  river  cuts 
down  its  new  valley  across  the  belt  of  hard  rock  that  is  to 
make  the  mountain  ridge,  the  valley  remains  narrow  for  a 
very  long  time  ;  but  elsewhere  the  valleys  of  the  trunk  and 


Fig. 139. 


Intrenched  Meanders  of 
the  Neckar 


274 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Fig.  140.    Transverse  and  Longitudinal  Streams 


branch  streams  widen 
rapidly  in  the  weaker 
rocks,  and  in  time  all 
the  hills  of  the  weak- 
rock  belts  are  worn 
away,  leaving  a  low- 
land on  each  side  of 
the  hard-rock  ridge, 
through  which  the 
water  gap  has  been 
cut,  as  in  Figure  141. 
This  explanation 
applies  to  the  Susque- 
hanna, cutting  gaps  in 
the  Allegheny  ridges, 
Figure  142,  and  to 
the  stream  that  has  cut  a  deep  passage  in  one  of  the  Alle- 
gheny ridges  in  Maryland,  shown  in  Plate  IX. 


Fig.  141.    Transverse  and  Longitudinal  Valleys 


Fig.  142.    Water  Gap  of  the  Susquehanna  above  Harrisburg,  Pennsylvania 

Where  must  one  stand  in  Figure  141  to  gain  a  view  like  that 
of  Figure  142  ?     How  many  water  gaps  are  shown  in  Figure  103  ? 


RIVERS  AND  VALLEYS  275 

QUESTIONS 

Sec.  134.  How  is  the  rainfall  of  a  region  disposed  of?  What  is 
ground  water  ?  Under  what  conditions  will  much  of  the  rainfall  be 
evaporated  into  the  air?  discharged  by  streams?  absorbed  by  the 
ground  ?     What  is  the  run-off  ?     Of  what  value  is  ground  water  ? 

135.  How  are  caverns  generally  formed  ?  What  is  a  sink  hole  ? 
What  effect  have  sink  holes  on  surface  streams  ?  Describe  an  under- 
ground stream.  Describe  the  animals  of  caverns.  What  is  the 
origin  of  the  Natural  bridge  of  Virginia? 

136.  What  is  a  spring?  Upon  what  does  the  variation  of  stream 
volume  depend?  Under  what  conditions  is  the  variation  small? 
Describe  the  movement  of  ground  water.  Where  is  it  found  at  a 
small  depth  ?  To  what  depth  should  wells  be  dug  or  bored  ?  Why 
is  spring  water  purer  than  stream  water  ? 

137.  What  is  an  Artesian  well  ?  How  is  its  water  supplied  ?  Name 
some  districts  where  such  wells  are  common.  What  is  the  relation 
of  certain  Artesian  wells  in  eastern  Maiyland  to  Chesapeake  bay  ? 

138.  Explain  hot  springs.  Why  are  they  commonly  charged  with 
mineral  salts  ?     Of  what  value  are  they  ?    Name  some  examples. 

139.  140.  What  is  a  geyser?  Where  are  the  most  famous  gey- 
sers ?    Describe  and  explain  the  action  of  geysers ;  of  mud  volcanoes. 

141.  Define  river,  river  system,  river  basin,  divide,  channel,  bed, 
banks.  What  is  meant  by  a  continental  divide?  by  undivided 
drainage?  by  subdivides?  What  features  of  a  river  system  have 
you  seen  illustrated  in  a  small  way? 

142.  Describe  a  river  flood.  Where  is  the  river-borne  waste 
laid  down?  How  is  a  river  supplied  after  a  flood  subsides?  How 
does  a  drought  affect  ground  water?  springs?  streams?  Compare 
the  streams  of  the  rainy  and  of  the  drier  parts  of  the  United  States. 

143.  Give  some  examples  of  the  work  of  rivers  from  earlier  chap- 
ters. Upon  what  does  the  depth  to  which  a  valley  may  be  cut 
depend  ?  How  do  slope  and  volume  affect  the  velocity  of  a  stream 
and  its  load  of  sediment  ?    Why  does  a  river  carry  more  sediment  at 


276  ELEMENTARY  PHYSICAL  GEOGRAPHY 

time  of  flood  ?  How  is  erosion  performed  by  rivers  ?  What  is  the 
source  of  the  rock  waste  borne  by  rivers  ?  In  what  sense  is  it  said 
that  "rivers  erode  their  valleys"?  Under  what  conditions  may  a 
river  be  called  young?   old?   mature? 

144.  How  is  the  course  of  a  young  river  determined?  What 
work  is  done  by  young  rivers?  What  are  the  characteristics  of 
young  rivers?  Describe  the  St.  Lawi'ence  system;  the  drainage  of 
the  Laurentian  highlands ;  that  of  the  region  of  the  great  African 
lakes.    What  changes  occur  as  a  river  passes  from  youth  to  maturity  ? 

145.  How  are  lakes  converted  into  rivers?  Illustrate  by  Lake 
Geneva.  In  what  part  .of  the  life  of  a  river  system  are  lakes  most 
common  ?  How  do  lakes  affect  the  transparency  and  the  steadiness 
of  flow  of  their  outflowing  streams?  Compare  the  Ohio  and  the 
St.  Lawrence  as  to  floods. 

146.  Where  are  falls  and  rapids  formed  in  young  rivers  ?  How  are 
gorges  formed  ?  Illustrate  by  the  gorge  of  the  Niagara ;  by  the  Yel- 
lowstone canyon.  How  do  differences  in  rock  structure  determine 
the  occurrence  of  falls  or  rapids  ?    What  uses  are  made  of  waterfalls  ? 

147.  Describe  a  torrent.  What  determines  the  least  slope  to 
which  a  river  can  wear  down  its  course  ?  Describe  a  graded  river. 
Where  have  graded  streams  a  relatively  strong  slope?  Why? 
Where  have  they  a  very  faint  slope  ?  Why  ?  State  the  slope  and 
the  load  of  the  lower  Mississippi. 

148.  Where  are  graded  reaches  first  developed  in  a  river  ?  Where 
do  rapids  survive  longest?  What  is  a  local  baselevel?  In  what 
condition  are  the  rivers  of  New  England  ?  What  other  region  has 
similar  rivers?  Describe  a  river  that  has  long  been  undisturbed. 
Describe  the  stream  slopes  in  a  well-graded  river  system.  How  do 
its  branches  join  its  trunk  ?     Why  are  they  thus  related  ? 

149.  Describe  the  valley  of  a  young  river.  What  disadvantages 
does  it  present  to  occupation  ?  How  do  floods  act  in  such  valleys  ? 
Illustrate  from  the  Allegheny  plateau.  How  is  a  valley  floor  wid- 
ened ?  What  changes  do  the  valley  sides  suffer  ?  What  advantages 
are  presented  by  a  widened  valley  ? 


RIYERS  AND  VALLEYS  277 

150.  Describe  the  action  of  a  winding  stream.  Describe  its  val- 
ley when  grade  is  reached.  What  changes  occur  after  grade  is 
reached  ?  Compare  the  outer  and  inner  sides  of  river  curves.  Where 
and  in  what  pattern  is  the  flood  plain  first  developed  ?  Describe  the 
later  changes  in  the  valley  spurs ;  in  the  flood  plain.  Where  is  the 
most  silt  laid  down  during  a  flood  ?  How  does  this  affect  the  form 
of  a  flood  plain  ?  How  does  a  heavy  load  of  waste  affect  the  behavior 
of  a  river  ?     Give  an  example. 

151.  How  does  a  light  load  affect  the  course  of  a  river  and  the 
slope  of  its  flood  plain  ?  What  are  meanders  ?  What,  is  the  deriva- 
tion of  this  term?  On  what  does  the  size  of  meanders  depend? 
How  does  their  form  vary  ?  How  has  the  course  of  the  Mississippi 
changed?  How  have  these  changes  affected  its  flood  plain?  .What 
is  an  oxbow  lake  ?  Describe  an  example.  How  is  the  shifting  of  a 
river  channel  checked  ?  How  are  flooded  rivers  restrained  ?  Describe 
the  effects  of  the  Mississippi  flood  of  1897.  Describe  the  Nita  crevasse. 

152.  153.  Describe  the  fan  of  the  Merced  river.  Why  is  irriga- 
tion needed  here?  How  is  it  favored?  Describe  the  fan  of  the 
Hoang-Ho,  and  its  relation  to  the  people  of  China.  Describe  a  river- 
made  plain.     Give  an  illustration  from  California. 

154.  How  are  deltas  formed  ?  What  is  the  relation  of  a  delta  to 
a  flood  plain  ?  What  are  distributaries  ?  Describe  some  examples. 
What  is  the  relation  of  deltas  to  tides  ?  Give  examples.  Why  are 
deltas  wanting  at  certain  river  mouths  ?  Give  examples.  What  is 
the  relation  of  large  deltas  to  population  ? 

155,  156.  What  are  the  features  of  mature  rivers  ?  Describe  the 
work  of  mature  rivers ;  the  change  from  a  mature  to  an  old  river ; 
an  old  river  system.     Why  is  it  unusual  to  find  old  rivers? 

157.  What  is  a  revived  river  ?  Describe  the  rivers  of  the  Pied- 
mont belt  in  Virginia.  Describe  the  valley  of  a  revived  meandering 
river.  Give  two  examples.  What  changes  may  happen  in  such 
valleys?    Illustrate  by  the  Neckar. 

158.  What  is  a  water  gap  ?  Give  an  example.  Explain  it.  What 
is  the  origin  of  the  lowland  upstream  from  a  water  gap  ? 


CHAPTER  IX 
DESERTS  AND  GLACIERS 

159.  Land  Forms  dependent  on  Climate.  —  In  regions 
of  ordinary  climate  the  snow  of  winter  melts  in  the  spring, 
and  the  droughts  of  summer  are  not  severe  enough  to  make 
the  surface  barren  by  preventing  plant  growth.  The  form 
of  such  regions  is  determined  largely  by  the  action  of 
streams  and  rivers,  whose  work  goes  on  steadily  along 
branches  and  trunk  so  that,  in  the  course  of  ages,  the 
land  surface  is  dissected  and  a  mature  system  of  branch- 
ing valleys  is  carved.  Many  examples  of  regions  of  this 
kind  have  been  given  in  the  descriptions  of  plains  and 
plateaus,  mountains  and  volcanoes. 

An  excellent  illustration  of  a  well-dissected  upland  is 
found  in  the  Ozark  plateau  of  southern  Missouri.  The 
once  even  plateau  has  been  transformed  into  a  succession 
of  rounded  hills  and  spurs  of  graceful  form,  separated  by  a 
multitude  of  branching  valleys.  The  maturely  dissected  sur- 
face has  much  less  strength  of  relief  than  the  plateau  of 
West  Virginia ;  its  slopes  are  usually  of  moderate  steepness  ; 
it  is  a  fertile  agricultural  district.  Villages  are  generally 
on  the  uplands,  for  most  of  the  valleys  are  as  yet  too  narrow 
to  attract  settlement.  Many  other  examples  might  be  named 
in  which  well-established  branching  valley  systems  testify 
to  the  long  duration  of  an  ordinary  or  normal  climate. 

278 


DESERTS  AND  GLACIERS  279 

111  certain  other  parts  of  the  world  the  climate  is  so  dry 
that  vegetation  is  scanty  or  wanting,  and  the  surface  is  left 
barren  and  desolate.  Here  streams  flow  only  at  rare  inter- 
vals, the  rivers  frequently  fail  to  reach  the  ocean,  and  the 
wind  becomes  an  important  means  of  moving  land  waste. 

In  still  other  parts  of  the  world  the  mean  annual  tem- 
perature is  so  low  that  the  snowfall  is  not  all  melted  away 


in  the  warm  season.  The  snow  thus  gathers  from  year  to 
year,  and,  as  it  thickens,  the  under  part  is  slowly  com- 
pacted into  ice.  The  ice  has  become  thick  enough  to 
behave  like  a  viscous  body  and  to  creep  slowly  down  the 
slope  of  the  land  until  it  enters  a  warmer  climate,  where 
it  melts  away.  Such  moving  sheets  or  streams  of  ice  are 
called  glaciers.  Regions  thus  covered  with  ice  and  snow 
are  even  more  barren  than  arid  deserts.  The  removal  of 
rock  waste  is  there  chiefly  performed  by  ice  instead  of  by 
rain  and  rivers. 


280  ELEMENTARY  PHYSICAL  GEOGRAPHY 

160.  Deserts.  —  It  has  been  explained  in  the  paragraphs 
on  rainfall  that  the  arid  deserts  of  the  world  occur  under 
the  drying  trade  winds,  on  the  slopes  and  lowlands  to  the 
leeward  of  high  mountain  ranges,  or  in  inclosed  continental 
interiors.  (See  page  71.)  The  interior  basins  of  Nevada 
and  Utah,  inclosed  from  moist  winds  by  the  ranges  of  the 
Pacific  slope,  fall  under  the  third  class,  although  they  are 
less  arid  than  many  parts  of  the  Sahara. 

All  of  these  deserts  are  hot  in  summer,  but  they  may  be 
cool  or  cold  in  winter.  They  should  therefore  be  thought 
of  as  prevailingly  dry  regions  which  may  be  hot  or  cold 
according  to  the  season  of  the  year.  The  deserts  of  cen- 
tral Asia  have  a  mean  January  temperature  of  only  10° 
or  20°  F. 

Rain  seldom  falls,  and  the  dry  air  parches  the  dusty, 
sandy,  or  stony  ground,  so  that  plant  life  in  deserts  is 
scanty,  though  it  is  rarely  altogether  absent. '  Rock  waste 
is  plentifully  exposed  on  open  spaces  between  the  scat- 
tered desert  plants,  instead  of  being  covered  by  a  close 
growth  of  grass,  bushes,  or  trees,  as  in  regions  of  more 
favorable  climate. 

Deserts  are  of  all  forms,  —  mountains,  plateaus,  and 
plains;  but  desert  plains  are  the  most  extensive.  The 
desolate  gray  forms  of  desert  mountains,  like  the  ranges 
of  northwest  Mexico  (Sonora)  and  of  northern  Chile 
(Atacama),  are  much'  less  picturesque  than  mountains 
with  snowy  summits  and  forested  flanks  in  a  moister 
climate;  but  the  wet-weather  torrents  of  desert  moun- 
tains have  furrowed  them  with  deep  ravines  like  those  of 
forested  mountains. 


DESERTS  AND  GLACIERS  281 

161.  Streams  of  Dry  Climates.  —  When  a  light  rain 
occurs  in  a  region  of  dry  climate  much  of  the  water 
returns  to  the  atmosphere  by  evaporation,  a  large  part  of 
the  remainder  sinks  into  the  thirsty  soil,  and  the  run-off  by 
streams  is  small.  Much  of  the  ground  water  evaporates 
underground  and  passes  out  from  the  soil  as  vapor,  instead 
of  coming  out  in  springs.  When  a  heavy  rain  occurs,  as 
occasionally  happens,  water  is  supplied  faster  than  it  can 
soak  into  the  ground,  surface  rills  form  everywhere,  and 
the  streams  are  quickly  flooded;  but  the  floods  soon  run 
away,  leaving  the  channels  empty  and  dry  again. 

The  streams  of  dry  regions  are,  therefore,  very  variable 
in  volume ;  active  for  a  while  after  a  rain,  almost  or  quite 
disappearing  in  the  long  dry  seasons ;  advancing  far  down 
their  lower  courses  when  in  flood,  then  dwindling  and 
withering  away  and  leaving  their  lower  channels  dry. 

In  the  Sahara  dry  water  courses,  known  as  wadies,  are 
commonly  used  for  roads,  as  their  gorges  frequently  offer 
graded  ways  through  rocky  uplands.  Death  by  drown- 
ing would  nowhere  be  so  little  expected  as  in  a  desert; 
but  it  sometimes  happens  that  a  caravan,  following  a  wady 
through  an  upland,  meets  a  down-rushing  flood,  and  before 
the  travelers  can  climb  the  steep  walls  of  the  gorge  they 
may  be  overwhelmed  and  drowned. 

In  parts  of  the  Rocky  mountain  region,  of  generally 
dry  climate,  heavy  rains  occasionally  fall  in  summer. 
Then  for  a  few  hours  the  dry  chanilels  are  flooded  with 
a  rushing  turbid  stream,  which  sweeps  away  the  waste  that 
has  been  washed  in  by  lighter  rains.  Camping  parties, 
pitching  their  tents  too  near  a  channel  that  is  almost 


282 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


dry  in  the  afternoon,  may  be  overwhelmed  by  a  rushing 
flood  at  night.  Opposite  the  mouths  of  canyons,  streams 
of  coarse  waste,  including  bowlders  weighing  many  tons, 
are  spread  forward  by  floods  from  cloud-bursts  in  the  moun- 
tains,—  "immense,  sudden,  deluging  rainstorms,  which  at 
rare  and  exceptional  moments  discharge  their  waters  into 


^^ 

"i  ,,. 

M 

III 

1           JICTE 

^^^^^^^^HH 

mi 

^B 

1 

1 

p 

IHwi'' " ''''''':''«'!^^^^^!|^H^|U 

Cg 

1 

1 

I^K 

W' 

JK 

i^H 

C^     ,^-  --^1 

IHH 

K: 

.^^^ 

.^..-J^^^^hI 

Fig.  145.    Flood  in  Cherry  Creek,  Denver,  Colorado 


one  of  these  mountain  gorges.  On  such  occasions  bowlders 
six  or  eight  feet  in  diameter  are  swept  down  the  canyon 
in  a  fearful  rush,  and  are  sometimes  carried  out  on  the 
.  .  .  slope  for  half  a  mile." 

Figure  145  illustrates  a  sudden  flood  in  Cherry  creek, 
where  it  passes  through  the  city  of  Denver,  Colorado. 
The  channel  of  the  creek  was  dry  half  an  hour  before 
this  raging  torrent  appeared. 


DESERTS  AND  GLACIERS  283 

Streams  that  are  supplied  by  springs  in  arid  uplands 
and  mountains  frequently  diminish  in  volume,  partly  by 
evaporation,  partly  by  sinking  into  the  ground,  as  they 
advance  over  desert  lowlands.  They  may  wither  away 
and  disappear  entirely  from  the  surface;  but  their  flow 
is  usually  continued  as  ground  water  for  some  distance 
beyond  their  visible  end.  Their  load  of  waste  is  spread 
on  the  surface  before  them  in  the  form  of  an  alluvial  fan. 
Many  such  streams  are  known  around  the  mountains  of 
Utah  and  Nevada.  The  depressions  between  the  ranges 
are  floored  with  fans  and  plains  of  waste  that  has  been 
washed  from  the  mountain  ravines  in  time  of  flood. 

162.  Bad  Lands.  —  Arid  regions  of  weak,  fine-textured 
strata  are  often  minutely  carved  by  the  wet-weather  rills 
and  rivulets  bordering  their  chief  valleys.  This  would  not 
happen  in  a  moister  climate,  for  there  the  abundant  plant 
growth  would  protect  the  surface  and  prevent  the  active 
run-off  of  the  wet-weather  rills;  but  in  an  arid  region, 
where  plants  are  few  or  wanting,  every  little  wet-weather 
rill  erodes  its  own  little  ravine  in  the  barren  surface. 

Western  Nebraska  offers  many  examples  of  uplands  that 
have  been  elaborately  dissected  in  this  way.  Plate  XII 
exhibits  the  delicately  carved  sides  of  a  young  valley  in  an 
even  upland.  Sharply  carved  forms  of  this  kind  are  known 
as  had  lands  because  of  the  difficulty  of  crossing  them. 

163.  Interior  Basins  and  Salt  Lakes.  —  The  larger  rivers 
of  interior  regions  do  not  entirely  wither  away  in  their  chan- 
nels, but  continue  until  they  reach  a  depression  or  basin  be- 
tween the  uplands.    There  the  waters  spread  out,  forming  a 


284  ELEMENTARY  PHYSICAL  GEOGRAPHY 

lake.  Evaporation  from  the  lake  surface  discharges  as  much 
water  into  the  air  as  is  received  from  the  inflowing  streams. 

In  regions  of  more  abundant  rainfall  the  streams  from 
a  moderate  drainage  area  suffice  to  fill  lake  basins  to  over- 
flowing. The  Great  lakes  of  the  St.  Lawrence  system 
gather  their  water  from  a  comparatively  small  area  around 
each  basin,  yet  they  are  always  full,  up  to  the  outlet  notch 
in  their  rim.  In  desert  regions  rainfall  is  so  scanty  and 
evaporation  is  so  active  that  the  streams  from  a  large 
drainage  area  may  form  only  a  shallow  lake,  occupying 
a  small  fraction  of  its  drainage  area. 

Lakes  of  the  latter  kind  are  usually  salt,  for  all  the  saline 
substances  gathered  in  small  quantity  by  their  rivers  accu- 
mulate in  the  lake  and  may  in  time  constitute  a  fifth  or 
even  a  third,  by  weight,  of  the  lake  contents. 

Great  Salt  lake  of  Utah,  with  about  eighteen  per  cent 
of  salt,  is  of  this  kind.  It  lies  on  the  lowest  part  of  the 
waste  plain  that  has  been  built  up  in  the  depression  among 
several  mountain  ranges.  Its  waters  are  so  dense  that  a 
man's  body  will  not  sink  beneath  the  surface.  The  Dead 
sea,  with  twenty-four  per  cent  of  salt,  is  one  of  the  most 
famous  salt  lakes,  occupying  a  long  narrow  depression  in 
Palestine.  Lake  Van,  in  eastern  Turkey,  containing  thirty- 
three  per  cent  of  salt,  is  the  densest  water  body  known. 

Interior  basins,  from  which  no  rivers  escape  to  the  sea, 
receive  the  waste  that  the  slopes  of  the  inclosing  moun- 
tains lose.  The  floors  of  the  basins  are  in  this  way  built 
up  and  smoothed.  By  the  wearing  down  of  the  moun- 
tains and  the  filling  of  the  basins  the  relief  of  the  region 
as  a  whole  is  decreased.     (See  Figure  144.) 


DESERTS  AND  GLACIERS  285 

The  level  of  the  Dead  sea  is  almost  1300  feet  below 
that  of  the  Mediterranean,  and  the  bottom  of  the  trough 
occupied  by  this  sea  is  about  1300  feet  deeper  still. 
Ravines  in  the  border  of  the  uplifted  plateaus  lead 
down  to  stony  fans  that  are  advancing  into  the  sea. 
The  great  depth  of  the  water  and  the  moderate  exten- 
sion of  the  fans  show  that  the  basin  contains  much  less 
waste  now  than  it  will  in  the  future. 

A  great  part  of  Persia  consists  of  large  basins  inclosed 
by  mountains  and  without  outlet  to  the  sea.  Long  waste 
slopes  stretch  forward  five  or  ten  miles  with  a  descent 
of  1000  or  2000  feet,  stony  near  the  mountain  flanks, 
and  gradually  becoming  finer  textured  and  more  nearly 
level  farther  away.  The  central  depressions  are  deserts 
of  drifting  sands,  with  occasional  salt  lakes.  The  popu- 
lation gathers  around  the  margins  of  the  basins  where  the 
dwindling  streams  are  still  running,  avoiding  the  rugged 
and  barren  mountains  on  the  one  hand,  and  the  unin- 
habitable central  plains  on  the  other. 

Central  Asia  repeats  the  same  conditions  on  a  still 
larger  scale.  The  basin  of  Eastern  Turkestan  includes 
in  its  central  part  many  low  ranges  that  have  been  half 
buried  with  waste  from  the  higher  inclosing  mountains. 
Many  rivers  flowing  from  the  mountain  rim  wither  on 
their  way  toward  the  chief  central  depression ;  only  the 
largest  river  (Tarim)  reaches  it,  there  spreading  out  in 
the  marshy  Lake  Lob.  The  chief  settlements  are  near 
the  border  of  the  basin,  where  the  larger  rivers  come  out 
from  the  mountains  and  where  their  waters  can  be  used 
for  irrigation. 


286  ELEMENTARY  PHYSICAL  GEOGRAPHY 

164.  Wind  Action  in  Deserts.  —  Where  the  land  surface 
is  covered  with  vegetation  the  wind  has  little  effect  on 
the  form  of  the  ground.  In  arid  regions  where  vegetation 
is  scanty  or  wanting  the  wind  becomes  a  powerful  agent 
of  change.  The  difference  of  wind  action  on  a  dusty  road 
and  on  a  grassy  field  may  be  taken  to  illustrate  the  con- 
trast between  wind  action  in  regions  of  dry  and  of  wet 
climate. 

Wind  storms  in  deserts  raise  the  finest  dust  high  into 
the  air,  drift  along  the  sand  at  the  bottom  of  the  current, 
and  rasp  the  unmoved  stones  and  ledges  with  the  drifted 
sand. 

Even  in  calm  weather  whirlwinds  are  of  daily  occur- 
rence in  deserts  during  the  hot  season.  They  are  formed 
by  the  whirling  ascent  of  air  that  has  been  heated  by  the 
action  of  sunshine  on  the  dry  bare  ground.  Before  the 
whirl  begins  the  existence  of  the  overheated  layer  of  sur- 
face air  is  often  indicated  by  a  mirage. 

Whirlwinds  may  raise  dust  more  than  a  thousand  feet 
into  the  air  and  drift- it  long  distances  before  it  settles. 
When  violent  winds  blow,  like  the  squalls  which  often 
precede  thunderstorms  in  a  moister  climate,  heavy  clouds 
of  sand  and  dust  are  raised  from  the  desert  surface,  dark- 
ening the  sky,  and  almost  suffocating  the  traveler  over- 
taken by  them. 

Vessels  in  the  Atlantic  west  of  the  Sahara  sometimes 
have  their  sails  reddened  with  dust  brought  by  the  trade 
wind  from  the  Sahara.  Rain  in  southern  Europe  is  occa- 
sionally reddened  with  dust  brought  by  storm  winds  from 
the  same  source.     It  has  been  estimated  that,  during  four 


DESERTS  AND  GLACIERS  287 

days  of  such  winds  in  March,  1901,  nearly  2,000,000  tons 
of  dust  from  the  Sahara  fell  on  central  Europe  ;  the  greater 
part  reached  the  ground  south  of  the  Alps,  but  some  of  the 
dust  was  observed  as  far  north  as  the  Baltic  sea.  East  of 
the  deserts  of  central  Asia  extensive  deposits  of  wind-borne 
dust  have  been  formed ;  they  constitute  some  of  the  most 
fertile  districts  in  the  Chinese  empire. 

Desert  mountains  and  uplands  are  so  well  exposed  to 
strong  winds  that  the  finer  particles  of  rock  waste  are 


Fig.  146.    Sand  Dunes  in  the  Sahara 

blown  from  them,  leaving  their  surface  rocky  and  stony. 
The  finer  particles  settle  chiefly  in  the  depressions  where 
the  winds  are  less  violent;  here  the  surface  is  sandy 
or  dusty. 

165.  Sand  Dunes.  —  When  the  rocks  of  a  desert  are  of 
a  kind,  like  granite,  that  affords  sand  on  weathering,  the 
wind  may  blow  the  sand  grains  into  drifts  or  dunes. 
Dunes  sometimes  grow  to  a  height  of  from  500  to  600 
feet.  Their  surface  may  be  delicately  rippled,  as  in 
Plate  XIII.  In  a  region  of  relatively  steady  winds  the 
sand  is  blown  up  the  windward  slope  and  carried  over 
the  crest ;  hence  the  dune  may  slowly  advance,  gradually 


288  ELEMENTARY  PHYSICAL  GEOGRAPHY 

changing  its  place  and  form.  Dunes  of  drifting  sand  are 
usually  more  barren  than  other  parts  of  a  desert. 

A  group  of  dunes  sometimes  advances  across  a  dry  val- 
ley, concealing  its  form  for  several  miles.  When  rain  falls 
the  stream  from  the  upper  part  of  the  valley  disappears  as 
it  enters  the  loose  sand  of  the  dunes. 

Sand  dunes  occur  also  on  low  coasts  where  the  winds 
frequently  blow  landward  across  a  sandy  beach.  The 
dunes  then  form"  a  belt  of  hills  a  little  inland  from  the 
beach,  as  will  be  again  referred  to  under  shore  forms. 

166.  Dry  Regions,  formerly  Moist.  —  In  some  regions 
now  arid,  marks  of  a  former  moist  climate  are  found. 
Certain  basins  now  almost  without  water  have  been  filled 
with  great  lakes,  even  to  overflowing;  the  former  shore 
lines  of  the  lakes  are  marked  by  cliffs,  beaches,  and  deltas, 
and  an  outlet  is  sometimes  traceable  in  a  trench  across  the 
lowest  pass  in  the  inclosing  highlands. 

The  basin  of  Great  Salt  lake  in  northwestern  Utah  in 
prehistoric  times  contained  a  much  larger  lake,  to  which 
the  name  of  an  explorer,  Bonneville,  has  been  given.  Its 
shore  lines  are  still  plainly  recorded  on  the  mountain  sides 
nearly  1000  feet  above  the  desert  plain  around  the  present 
lake ;  the  foreground  of  Figure  86  shows  an  extensive  beach 
of  this  lake.  The  channel  of  an  outlet  leads  northward 
across  a  pass  to  the  basin  of  Snake  river ;  hence  the  former 
lake  must  have  been  fresh.  The  change  from  the  moister 
climate  of  Lake  Bonneville  time  to  the  drier  climate  of 
to-day  has  caused  the  almost  complete  disappearance  of  the 
lake  waters,  revealing  the  sediments  of  the  lake  floor  in 


DESERTS  AND  GLACIERS 


289 


an  arid  plain.     The  ancient  lake  deltas  are  now  trenched 
by  the  streams  that  built  them. 

Another  extensive  lake  (Lahontan)  of  very  irregular 
outline  and  several  smaller  lakes  once  occupied  the  now 
desert  basins  of  western  Nevada. 


Fig.  147.    Lakes  Bonneville  and  Lahontan 


Compare  the  area  of  Lake  Bonneville  and  that  of  Great  Salt  lake 
(fine  and  coarse  dots,  Figure  147).  How  long  is  Lake  Bonneville 
from  north  to  south  ?  How  long  is  Great  Salt  lake  from  northwest 
to  southeast  ?     (Scale  of  figure,  200  miles  to  an  inch.) 

The  causes  of  climatic  changes  of  this  kind  are  little 
understood,  but  their  geographical  consequences  are  of 
great  importance.  Extensive  lakes  among  forest-clad 
slopes  have  been  replaced  by  desert  plains  between  arid 
mountains. 


290  ELEMENTARY  PHYSICAL  GEOGRAPHY 

167.  Salinas.  —  Certain  basins  that  formerly  contained 
salt  lakes  have  now  been  more  or  less  completely  dried 
out,  leaving  marshy  or  dry  plains  of  salt,  known  as  salinaSy 
in  the  central  depressions,  avoided  by  all  plant  and  animal 
life. 

The  Bolivian  table-land,  a  lofty  waste-filled  basin  lying 
between  two  great  ranges  of  the  Andes,  holds  Lake  Titi- 
caca  in  its  northern  part  at  an  altitude  of  12,500  feet. 
The  outflowing  stream  runs  100  miles  southeast  to  a 
marshy  salina,  fifty  miles  long.  The  water  not  evaporated 
here  flows  southwest  and  is  lost  in  a  broad  salina  of  daz- 
zling white  surface.  Somewhat  farther  south  is  a  more 
extensive  sahna,  4000  square  miles  in  area,  a  white  and 
level  plain  covered  with  a  layer  of  salt  about  four  feet 
thick,  impassable  when  wet,  but  firm  in  the  dry  season. 

Salt  lakes  and  salinas  yield  common  salt  and  other  min- 
erals of  commercial  value.  Great  Salt  lake  is  estimated 
to  contain  400,000,000  tons  of  salt.  These  products 
would  be  of  greater  utility  if  they  did  not  so  generally 
occur  in  thinly  populated  desert  regions. 

168.  Ice  Sheets  and  Ice  Streams.  —  In  the  polar  regions 
the  temperature  even  in  the  lower  atmosphere  is  so  low  that 
snow  and  ice  cover  much  of  the  land  all  the  year  round, 
even  close  to  sea  level,  cloaking  the  ground  with  ice 
sheets.  In  the  temperate  and  torrid  zones  it  is  only  on 
mountains  that  the  temperature  is  low  enough  for  snow 
to  be  more  abundant  than  rain,  so  that  snow  fields  are 
formed  on  the  higher  slopes  and  ice  streams  in  the  upper 
valleys. 


DESERTS  AND  GLACIERS  291 

During  winter  in  the  northern  United  States  there  are 
frequent  examples  of  the  formation  of  small  short-lived 
ice  sheets,  after  a  succiBSsion  of  snowstorms  with  prevalent 
cold  weather  and  occasional  thaws.  Such  an  ice  sheet  is 
not  thick  enough  to  move  ;  but  if  it  should  grow  year  after 
year  to  a  thickness  of  1000  or  more  feet,  it  would  slowly 
move  outward  from  the  region  of  greatest  height  and 
thickness  to  lower  ground  in  a  milder  climate.  This  is 
because  ice  is  not  perfectly  solid;  it  moves  toward  its 
unsupported  border  very  much  as  a  thick  mass  of  paste 
would  move,  but  much  more  slowly. 

169.  Antarctic  Ice  Cap.  —  A  few  explorers  of  the  far 
southern  ocean  have  discovered  a  great  ice  sheet  ending 
in  cliffs  that  rise  from  100  to  180  feet  above  the  sea.  No 
land  was  seen  back  from  the  top  of  the  cliffs. 

Although  as  yet  known  only  on  one  side  of  the  south 
pole,  the  ice  sheet  is  thought  to  form  a  polar  ice  cap,  per- 
haps 1000  miles  in  diameter.  There  may  be  some  land  on 
which  the  cap  rests ;  but  it  is  believed  that  much  of  it  lies 
on  the  sea  bottom.  It  must  tend  to  thicken  from  snow 
supply  over  its  desert  plateaulike  center;  but  it  slowly 
creeps  toward  the  free  seaward  margin,  where  great  tables 
of  ice  break  off  and  float  away  as  icebergs.  As  far  as  this 
desolate  region  has  been  explored  it  is  uninhabited. 

170.  The  Greenland  Ice  Sheet.  —  Greenland  is  covered 
by  a  heavy  sheet  of  ice,  measuring  about  1500  miles  north 
and  south  and  from  300  to  600  east  and  west.  It  has  a 
slightly  convex  surface  and  probably  rises  to  a  height 
of  9000  feet  in  the  central  part.     The  ice  sheet  conceals 


292  ELEMENTARY  PHYSICAL  GEOGRAPHY 

the  hills  and  mountains  except  near  the  margin,  where 
the  sheet  is  thinner;  here  occasional  rocky  summits  rise 
above  the  surface  like  islands  in  a  frozen  sea. 

Some  of  the  Greenland  glaciers  (arms  of  the  ice  sheet 
descending  toward  or  into  the  sea)  are  from  ten  to  fifty 
miles  broad.  Their  forward  movement  is  from  twenty 
to  fifty  feet  a  day.  Many  icebergs  are  formed  of  great 
fragments  broken  from  their  front.  The  interior  of  the 
ice  sheet  is  a  monotonous  desert  of  snow  and  ice,  now 
melting  and  becoming  almost  impassable,  now  freezing 
over  or  receiving  a  new  layer  of  snow. 

The  only  inhabitants  of  this  great  cold  desert  are  a 
minute  worm  and  a  simple  microscopic  plant  that  some- 
times gives  a  red  color  to  snow.  The  Eskimos  of  Green- 
land live  on  the  narrow  belt  of  land  between  the  ice  sheet 
and  the  shore. 

171.  Alpine  Glaciers.  —  Glaciers  of  the  Alpine  type  flow 
slowly  down  in  streamlike  tongues  from  snow  basins  in  the 
valley  heads  between  lofty  peaks  and  ridges. 

The  end  of  a  glacier,  melting  as  the  ice  descends  to  a 
milder  climate  than  that  of  its  gathering  ground,  often 
reaches  below  the  tree  line.  Glaciers  of  this  kind  occur  in 
the  Alps,  the  Caucasus  and  Himalaya  mountains  of  the 
Old  World,  and  in  the  mountains  of  Canada,  Alaska, 
and  Patagonia  in  the  New  World.  In  Alaska  many  of 
the  glaciers  descend  to  the  sea.  The  front  of  the  Muir 
glacier,  Plate  XIV,  breaks  ofP  in  cliffs  200  feet  high. 

A  glacier  moves  faster  along  the  middle  surface  line 
than  at  its  sides  or  bottom,  thus  resembling  a  river.     The 


DESERTS  AND  GLACIERS 


293 


movement  of  Alpine  glaciers  is  on  the  average  from  100 
to  500  feet  a  year. 

Glaciers  press  heavily  on  their  beds,  dragging  rock 
waste  beneath  them  and  scouring  the  bed-rock  clean  and 
smooth.  Loose  grains  and  fragments  of  rock,  dragged  along 
by  the  ice,  scratch  and  groove  the  smoothed  rock  surface. 
The  rock  waste 
thus  scoured  from 
the  ice  floor,  as 
well  as  that  torn 
from  projecting 
ledges  and  that 
received  in  rock 
slides  and  ava- 
lanches from  sur- 
mounting slopes, 
is  dragged  or  car- 
ried along  by  the 
ice  and  laid  down 
around  its  lower 
margin  or  at  its 
end,    or    washed 


FiQ.  148.    Rosegg  Glacier  in  the  Alps 


away  by  the  stream  that  issues  from  beneath  the  ice. 
Great  bowlders  may  be  carried  on  the  ice. 

The  ridge  of  rock  waste  that  is  ordinarily  formed  around 
the  end  of  a  glacier  is  called  a  terminal  moraine ;  one  is 
shown  in  Figure  148.  Note  the  moraine  that  trails  down 
on  the  Rosegg  glacier  from  a  rocky  spur  between  two  of 
its  upper  snow  basins.  It  is  called  a  medial  moraine. 
Why  does  it  not  follow  the  middle  of  the  glacier? 


294 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Describe  the  medial  moraine  of  the  Viesch  (pron.  feesh)  gla- 
cier, Figure  149.  From  how  many  snow  basins  is  this  glacier 
supplied  ? 

Large  glaciers  are  sometimes  so  heavily  covered  with 
moraines  near  their  lower  end  that  a  plant-bearing  soil  is 

formed  upon  them.  Pas- 
turage is  found  for  the 
flocks  of  the  mountaineers 
in  the  Himalayas  on  cer- 
tain grass-covered  mo- 
raines ov'erlying  the  ice. 
Some  Alaskan  glaciers 
bear  large  forests  on  the 
moraines  near  their  ends. 
Water  received  from 
side  streams  and  supplied 
from  melting  ice  gathers 
beneath  a  glacier  and 
issues  from  an  ice  cave 
at  its  end.  The  water  is 
usually  whitened  by  fine 
"rock  flour"  ground 
beneath  the  ice. 


Fig.  149.    Viesch  Glacier  in  the  Alps 


172.  The  Work  of  Ancient  Glaciers  and  Ice  Sheets. — Cer- 
tain parts  of  the  world  show  the  marks  of  ancient  glacial 
action,  although  the  climate  there  to-day  does  not  allow 
snow  to  remain  on  the  ground  through  the  summer. 

Ancient  glaciers  occupied  certain  valleys  in  the  Rocky 
mountains  of  Colorado  and  in  the  Sierra  Nevada  of- Califor- 
nia. Great  glaciers  descending  from  the  high  Sierra  into  the 


DESERTS  AND  GLACIERS 


295 


desert  lowland  in  eastern  California  built  strong  moraines 
forward  from  the  mountain  base  at  the  mouth  of  the  valley. 

Compare  the  glacier  that  once  occupied  the  valley  in  Figure  150 
with  the  Rosegg  glacier,  Figure  148. 

Around  the  border  of  the  Alps  the  lower  land  near  the  out- 
let of  the  chief  valleys  is  often  inclosed  for  ten  or  twenty 
miles  from  the  mountains  by  a  belt  of  hilly  morainic  ridges. 
The  ancient  glaciers  that  descended  southeast  from  Mt. 
Blanc  to  the  river- 
made  plain  of  the 
Po  built  a  huge 
terminal  moraine, 
whose  ridges  rise 
froml000tol500 
feet  above  the 
plain  and  inclose 
a  great  amphi- 
theater. 

The  most  ex- 
tensive ice  sheets 
of  the  fflacial 

"  Fig.  150.  Glacial  Moraines,  Sierra  Nevada,  California 

period  were  those 

that  spread  outward  from  the  highlands  of  Canada  across 
the  basins  of  the  Great  lakes  upon  the  northern  part  of  the 
United  States,  and  from  the  highlands  of  Scandinavia  across 
the  Baltic  upon  northern  Germany.     (See  Figure  144.) 

The  highlands  of  eastern  Canada, — the  Laurentian  high- 
lands, —  whence  the  ice  sheets  moved  out  to  the  surround- 
ing regions,  show  much  bare  rock,  clean  scoured  or  covered 


296 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


by  a  tliin,  stony,  infertile  soiL  The  hollows  between  the 
rounded  rocky  hills  were  often  deepened  by  the  ice,  so  that 
they  now  hold  lakes  or  swamps,  large  and  small.  Besides 
many  such  lakes  in  rock  basins,  others  are  held  behind 
barriei-s  of  rock  waste  or  drift  that  was  left  irregularly 
over  the  surface  when  the  ice  melted  away. 


Fig.  151.    Glaciated  Area  of  the  Northern  United  States 

Much  of  the  rock  waste  that  has  been  swept  from 
Canada  by  ice  action  is  now  found  spread  out  in  smooth 
plains,  forming  the  fertile  prairies  south  of  the  Great 
lakes.  Rock  waste  that  has  thus  been  dragged  along  by 
ice  action  or  washed  along  under  or  in  front  of  the  ice  by 
streams  is  known  by  the  general  name  of  glacial  drift. 

The  Scandinavian  highlands  and  the  lowlands  of  north- 
ern Germany  exhibit  the  same  relation  to  ancient  glaciation 
that  has  just  been  described  for  the  Laurentian  highlands 
of  Canada  and  the  states  bordering  the  Great  lakes.  The 
highlands  are  left  with  scanty  soil  and  much  bare  rock ; 


DESERTS  AND  GLACIERS 


297 


the  lowlands  are  sheeted  over  with  drift,  much  of  which 
is  fertile  fanning  country.  The  highlands  remain  in  great 
part  a  wilderness,  although  scattered  farms  and  small 
villages  are  found  in  the  valleys.  The  lowland  plain  has 
a  large  agricultural  population  and  many  busy  cities. 

Among  the  most  characteristic  results  of  ancient  glacial 
action  are  the  rounded  shapes  of  scoured  ledges.  Figure 
152,  and  the  irregular  surface  of  the  moraines,  Figui'e  153. 


Fig.  152.    Ice-Worn  Roclcs,  Coast  of  Maine 


Terminal  moraines  of  stones,  gravel,  and  sand  are 
strongly  developed  in  the  states  south  of  the  Great 
lakes.  They  form  belts  of  hills  commonly  from  three 
to  ten  miles  wide ;  the  hills  are  from  fifty  to  two  hundred 
feet  high.  The  moraines  are  sometimes  very  uneven, 
with  so  many  stony  mounds  and  marshy  hollows  as  to 
present  a  formidable  barrier  to  travel.  One  may  easily 
lose  his  way  on  such  an  undulating  surface,  where  the 
hilLs  are  all  much  alike  and  where  no  conspicuous  land- 
marks serve  as  guides. 


298 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Morainic  hills   are  frequently  dotted   over  with   large 
rocks  or  bowlders,  large  and  small,   brought  from  some 


Fig.  153.    Glacial  Moraines,  Nortli  Dakota 

more  or  less  distant  ledges  by  the  ice;  the  bowlders  are 
frequently  unlike  the  rock   on  which  the  moraine  lies. 


Fig.  154.    A  Glacial  Bowlder 


Glacial  bowlders  are  so  plentiful  in  some  pai-ts  of  New 
England  as  to  make  the  land  there  almost  worthless. 


DESERTS  AND  GLACIERS 


299 


173.  Drumlins.  —  In  some  districts  the  rock  waste  has 
been  left  beneath  the  ice  sheet  in  arched,  oval  hills 
called  drumlins,  commonly  half  a  mile  or  more  long  and 
from  100  to  200  feet  high,  easily  recognized  when  once 
known.  They  may  be  compared  to  sand  bars  in  rivers  or 
to  sand  dunes  under  the  wind. 


Fig.  155.     A  iJrmimii,  Massacmiseiis 


174.  Valleys,  Lakes,  and  Waterfalls  in  Regions  of  Ancient 
Glaciers. — Some  of  the  ancient  glaciers  of  mountain  regions 
were  very  massive,  from  2000  to  5000  feet  thick,  and  moved 
with  relative  rapidity  down  channels  of  rapid  descent ;  here 
glacial  erosion  was  most  intense.  The  channels  thus  occu- 
pied are  now  seen  as  broad  troughlike  valleys  with  steep 
walls,  deepened  from  500  to  1000  feet  or  more  beneath 
the  side  valleys  that  once  joined  them  at  even  grade.  The 
streams  from  the  side  valleys  plunge  down  the  rocky  walls 
of  the  deepened  main  valley,  forming  fine  waterfalls.  Dis- 
cordant side  valleys  of  this  kind  are  called  hanging  valleys. 

Many  hanging  valleys  are  found  in  the  Alps  and  in  the 
mountains  of  Norway  and  Alaska;  in  the  latter  regions 


300 


ELEMENTARY  PHYSICAL   GEOGRAPHY 


the  deepened  main  valley  is  usually  occupied  by  an  arm  of 
the  sea,  called  a  fiord.     (See  page  320.) 

The  rivers  of  a  region  that  has  been  oven-idden  by  an 
ice  sheet  are  often  greatly  disordered.      At  one  place  a 


Fig.  156.    A  Side  Valley  hanging  over  the  Valley  of  the  Ticino, 
Southern  Alps 


valley  floor  may  be  scoured  out,  producing  a  rock  basin. 
Lakes  occupying  such  basins  have  been  mentioned  as  com- 
mon in  the  rocky  highlands  of  eastern  Canada.  At  another 
place  the  irregular  distribution  of  rock  waste  or  drift  may 


DESERTS  AND  GLACIERS  301 

turn  a  stream  to  a  new  course,  where  it  is  now  seen  cut- 
ting a  steep-walled  gorge  with  many  rapids  and  falls.  A 
lake  is  often  formed  upstream  from  the  drift  barrier. 

The  Adirondacks  resemble  the  Black  mountains  of  North 
Carolina  in  being  dissected,  subdued  mountains,  but  the 
northern    group    possesses    numerous    lakes    and    gorges 


Fia.  157.    Lake  in  the  Adirondacks,  New  York 

("  chasms  ")  which  are  wanting  in  the  southern  group.  These 
peculiarities  result  from  glacial  action,  which  the  Adiron- 
dacks suffered  in  common  with  the  other  northern  parts  of 
the  country,  but  which  the  southern  mountains  escaped. 

When  a  river  is  displaced  by  barriers  of  glacial  drift 
it  must  carve  a  new  channel.  Before  the  time  of  the  ice 
action  the  river  may  have  had  a  well-graded  course ;  now 
its  flow  is  interrupted  by  falls  and  rocky  rapids.  Hence 
the  displaced  streams  of  glaciated  regions  supply  much 
water  power  for  mills  and  factories. 


302  ELEMENTARY  PHYSICAL  GEOGRAPHY 

Many  rapids  and  falls  of  this  kind  occur  in  the  streams 
of  the  northern  United  States  and  Canada.  It  must  be  con- 
cluded that  the  streams  have  not  yet  had  time  to  establish 
graded  courses  since  the  ice  melted  away,  and  therefore 
that  the  ice  sheet  covered  the  country  not  long  ago,  as 
streams  measure  time,  even  though  it  was  thousands  of 
years  ago,  as  time  is  counted  by  man. 

The  Merrimac  is  a  famous  river  of  this  kind.  Its  falls 
at  Manchester,  Lowell,  and  Lawrence  have  determined  the 
growth  of  great  manufacturing  cities.  Rochester,  Grand 
Rapids,  Minneapolis,  and  many  other  important  cities 
have  grown  up  at  the  side  of  falls  on  rivers  that  have 
been  turned  from  their  former  channels  by  glacial  drift. 

QUESTIONS 

Sec.  159.  What  is  meant  by  an  ordinary  climate  ?  How  are  land 
forms  carved  in  regions  of  ordinary  climate  ?  What  are  the  condi- 
tions of  a  land  surface  in  an  arid  climate  ?   in  a  cold  climate  ? 

160.  How  are  arid  deserts  related  to  the  wind  system  ?  Consider 
their  climate  as  to  heat,  cold,  and  dryness.  Describe  their  surface 
as  to  vegetation  and  rock  waste.     What  are  the  forms  of  deserts? 

161.  How  is  rainfall  disposed  of  in  a  dry  climate  ?  Describe  the 
streams  of  dry  regions.  What  is  a  wady?  What  danger  attends 
the  use  of  a  wady  as  a  roadway  ?  Describe  the  floods  of  the  drier 
parts  of  the  Rocky  mountain  region.  Describe  a  flood  at  Denver. 
How  may  streams  end  in  desert  lowlands  ?  What  becomes  of  their 
load  of  waste  ?     Where  is  their  flow  continued  ? 

162.  163.  Under  what  conditions  are  bad  lands  formed? 
Describe  their  form.  Where  do  they  occur  ?  What  becomes  of  the 
larger  rivers  of  interior  basins?  What  is  the  relation  of  inflow  and 
evaporation  in  lakes  without  outlets  ?  in  lakes  with  outlets  ?  Com- 
pare the  lake  area  with  the  drainage  area  in  the  two  cases.     Why 


DESERTS  AND  GLACIERS  303 

are  lakes  without  outlets  usually  salt?  Describe  Great  Salt  lake; 
the  Dead  sea.  How  is  the  form  of  interior  basins  changed  ?  Describe 
the  basin  of  the  Dead  sea;  the  basins  of  Persia;  of  central  Asia. 

164,  165.  Compare  wind  action  on  plant-covered  and  on  barren 
surfaces.  Describe  the  action  of  whirlwinds  in  arid  regions;  of 
violent  winds.  How  far  is  dust  carried  by  the  wind?  Where  do 
deposits  of  wind-borne  dust  occur  ?  Describe  sand  dunes  as  to  origin, 
height,  form,  movement.     Describe  the  dunes  of  coasts. 

166,  167.  Describe  the  ancient  shore  lines  of  the  Great  Salt  lake 
basin.  "What  do  they  prove  ?  Describe  another  similar  example  in 
Nevada.  How  do  the  two  differ?  What  is  the  present  condition 
of  these  two  basins?     What  are  salinas?     Describe  an  example. 

168,  169,  170.  Where  do  ice  sheets  occur?  When  may  a  short- 
lived ice  sheet  be  seen?  Describe  the  movement  of  an  ice  sheet. 
What  is  known  and  what  is  supposed  about  the  Antarctic  ice  cap  ? 
Describe  the  Greenland  ice  sheet.  How  are  glaciers  and  icebergs 
related  to  this  ice  sheet  ?    Where  do  the  Eskimos  of  Greenland  live  ? 

171.  Describe  a  glacier  of  the  Alpine  type.  Where  do  such 
glaciers  occur?  How  does  a  glacier  move?  What  work  does  it 
perform?  Describe  a  terminal  moraine  ;  a  medial  moraine.  State 
the  relation  of  vegetation  to  certain  moraines. 

172,  173.  How  has  the  occurrence  of  ancient  glaciers  been  discov- 
ered ?  Where  have  such  glaciers  existed  ?  What  remains  have  they 
left  ?  Where  did  the  most  extensive  ancient  ice  sheets  occur  ?  What 
effect  was  produced  by  the  North  American  ice  sheet  in  eastern  Can- 
ada ?  in  the  northeastern  United  States  ?  What  is  glacial  drift  ? 
Describe  the  effects  of  the  ancient  ice  sheet  of  northwestern  Europe. 
Describe  the  terminal  moraines  south  of  the  Great  lakes.  What  are 
glacial  bowlders  ?     Where  are  they  plentiful  ?     What  are  drumlins  ? 

174.  What  are  hanging  valleys?  Explain  them.  Where  do  they 
occur  ?  What  effect  have  ancient  ice  sheets  had  on  drainage  ? 
Describe  the  drainage  of  the  Laurentian  highlands.  Compare  the 
Adirondacks  and  the  Black  mountains.  What  effect  have  displaced 
streams  on  industries?    Name  some  examples. 


CHAPTER   X 
SHORE  LINES 

175.  The  Border  of  the  Lands  —  Next  to  the  prospect 
gained  from  a  lofty  mountain,  the  view  of  the  sea  from 
the  border  of  a  highland  is  the  most  inspiring  sight 
that  the  earth  offers.  To  the  traveler  from  an  inland 
country  it  is  as  if  the  shore  line  marked  the  beginning 
of  a  new  kind  of  world.  There  is  the  mystery  of  the 
distant  horizon,  far  beyond  which  strange  lands  are  hid- 
den. There  is  the  unceasing  movement  of  the  waves  as 
they  roll  upon  the  beach,  and  of  the  tides  as  they  slowly 
rise  and  fall ;  and  the  thought  comes  that  thus  the  ocean 
has  been  rolling  in  waves,  rising  and  falling  in  tides, 
ever  since  the  lands  and  the  waters  were  divided.  With 
the  sight  of  the  vast  ocean  comes  the  thought  of  unend- 
ing time. 

While  the  surface  of  the  land  has  been  for  ages 
attacked  by  rain  and  rivers,  the  border  of  the  land  has 
been  attacked  by  the  sea.  The  sun  warms  the  air  in 
the  torrid  zone,  and  thus  the  general  circulation  of  the 
atmosphere  is  established.  The  winds  beat  on  the  ocean 
and  form  waves,  and  the  waves  run  ashore  and  dash  in 
surf  upon  the  lands.  The  border  of  the  land  is  worn 
back  under  so  constant  an  attack,  and  the  waste  taken 
from  it  by  the  surf,  as  well  as  that  washed  into  the  sea 

304 


SHORE  LINES 


305 


by  rivers,  is  slowly  carried  away  into  deeper  water  by  the 
waves,  the  currents,  and  the  tides.  In  time  the  area  of 
the  land  would  be  greatly  reduced  by  the  invasion  of  the 
sea,  were  it  not  for  gradual  uplifts  by  which  the  land  is 
now  and  then,  here  and  there,  renewed. 


Fig.  158.    Sea  Cliffs,  Grand  M.i; 


176.  The  Work  of  the  Sea  on  the  Shore.  — Where  the 
border  or  coast  of  the  land  dips  under  the  sea  the  water 
lies  against  it  and  marks  the  shore  line.  The  waves  and 
other  agents  work  upon  the  shore  and  produce  changes 
in  its  form.  Hence  the  outline  of  any  shore  line  depends, 
in  the  first  place,  on  the  form  that  the  land  had  when  its 
present  attitude  with  respect  to  the  sea  .was  taken,  and 
in  the  second  place  on  the  changes  afterward  made  by 
the  shore  processes. 


306  ELEMENTARY  PHYSICAL  GEOGRAPHY 

The  agitation  of  sea  water  in  waves  is  greatest  at  the 
sea  surface  and  gradually  decreases  downward;  but  the 
large  waves  cause  some  slight  disturbance  even  at  depths 
of  several  hundred  feet.  The  movement  of  water  in 
waves  is  not  steadily  forward  in  the  direction  in  which 
the  waves  travel,  but  repeatedly  to  and  fro  over  small 
distances.  The  larger  the  waves  and  the  shallower  the 
water,  the  greater  effect  their  agitation  has  on  the  bottom. 
Fragments  of  rock,  large  and  small,  are  thus  moved  back 
and  forth  according  to  their  size  and  to  the  strength  of 
the  waves.  The  fragments  wear  each  other  as  well  as 
the  rocky  ledges  on  which  they  are  rolled  and  thrown. 
Thus  the  edge  of  the  land  is  worn  back  by  the  sea,  the 
shallower  parts  of  the  sea  are  slowly  deepened,  and  the 
waste  is  slowly  removed  to  deeper  water  offshore.  Little 
work  of  this  kind  is  done  in  calm  or  fair  weather;  but 
during  storms  the  processes  of  grinding  and  transporta- 
tion are  actively  at  work,  shaping  the  shore  line  and  the 
shallow  sea  bottom. 

The  currents  of  shore  waters  are  chiefly  of  tidal  origin, 
but  they  are  also  sometimes  parts  of  the  general  circulation 
of  the  ocean.  Except  in  narrow  channels,  they  are  seldom 
strong  enough,  unaided,  to  move  the  waste  that  is  strewn 
over  the  bottom ;  but  when  the  waste  is  jostled  by  waves 
it  slowly  shifts  along  in  the  direction  of  the  current. 

If  deep  water  reaches  close  to  the  land,  the  waves  spend 
most  of  their  strength  close  to  the  shore  line,  breaking  vio- 
lently on  the  headlands,  whence  they  sweep  loose  material 
out  to  the  deeper  bottom ;  there  it  rests  in  comparative  quiet. 
Bare  rock  is  abundantly  exposed  on  shores  of  this  kind. 


SHORE  LINES  307 

If  the  land  descends  slowly  under  the  sea,  the  shore  is 
fronted  by  shoal  water ;  then  much  of  the  strength  of  the 
waves  is  spent  on  the  shelving  bottom  before  they  reach 
the  shore  line.  Rock  waste  is  so  slowly  removed  from  a 
shore  line  of  this  kind  that  beaches  of  gravel  and  sand 
are  commonly  strewn  along  it ;  the  waters  offshore  become 
somewhat  turbid  during  storms  with  fine  waste  raised  by 
strong  waves  from  the  shallow  bottom. 

177.  Different  Kinds  of  Shore  Lines.  —  Two  kinds  of 
shore  lines  have  already  been  described.  In  one  the  sea 
lies  upon  a  smooth  coastal  plain  that  was  once  a  sea  bot- 
tom (page  144);  in  the  other  it  lies  on  the  flanks  of  a 
depressed  mountain  range  (page  211).  These  two  kinds 
are  the  types  for  many  other  examples. 

Shore  lines  of  the  first  kind  are  smooth  and  simple,  and 
are  bordered  by  shallow  water.  Shore  lines  of  the  second 
kind  are  irregular  and  are  generally  bordered  by  deep 
water.  Those  of  the  first  kind  border  lowlands  of  weak 
strata ;  they  have  few  good  harbors  and  hence  they  do  not 
offer  good  opportunity  for  traffic  between  land  and  sea. 
Those  of  the  second  kind  generally  have  rocky  headlands 
and  islands  inclosing  protected  bays,  where  harbors  are 
numerous  and  trading  settlements  are  favored. 

178.  Shore  Lines  of  the  First  Kind.  —  The  low  plain  of 
Buenos  Aires  dips  gently  beneath  the  sea,  whose  waters 
are  shallow  for  many  miles  off  the  simple  shore  line. 
Large  vessels  cannot  approach  close  to  the  land,  except 
where  an  artificial  harbor  has  been  dredged  out. 


308  ELEMENTARY  PHYSICAL  GEOGRAPHY 

When  storm  winds  blow  from  the  sea  they  sweep  the 
water  upon  the  low  coast  and  cause  destructive  sea  floods ; 
dikes  are  built  along  certain  parts  of  the  shore  to  keep 
the  waters  off. 

The  waves  along  the  shallow  shores  of  lowlands  beat 
up  the  bottom  sands  and  in  time  build  offshore  sand  reefs 
inclosing  narrow  lagoons.  The  movement  of  currents  along 
the  sand  reef  forms  a  beach,  straight  or  gently  curved  on 
its  seaward  side.  On-shore  winds  blow  sand  from  the 
beach  and  build  sand  hills  or  dunes  of  irregular  form, 
sometimes  fifty  or  one  hundred  feet  high,  on  the  reef. 
Flood  and  ebb  tidal  currents  maintain  passages,  called 
inlets,  through  the  reef,  as  at  i>.  Figure  159. 

Sediments  are  brought  into  the  lagoons  by  streams  from 
the  land,  and,  with  the  aid  of  salt-water  plants,  the  shallow 
lagoons  are  gradually  filled  and  converted  into  salt  marshes 
at  high-tide  level.  Sand  reefs,  lagoons,  and  marshes  are 
plentiful  along  the  Atlantic  and  Gulf  coast  of  the  United 
States. 

A  sand  reef  is  slowly  worn  back  by  the  action  of  the 
surf  on  its  beach.  The  dune  sands  are  slowly  blown  back 
into  the  narrowing  lagoon  or  upon  the  lagoon  marsh.  At 
last  the  lagoon  and  its  marsh  disappear,  and  the  mainland 
is  directly  attacked  and  cut  back  in  a  low  bluff.  The 
retreat  of  the  sand  reefs  may  be  more  rapid  on  one  stretch 
of  the  shore  than  on  another;  thus  one  part,  CA,  Fig- 
ure 159,  may  have  a  bluff  cut  in  the  mainland,  while 
another  part,  AB,  is  still  fronted  by  reef  and  lagoon. 

The  coast  of  New  Jersey  is  fronted  by  long  sand  reefs 
inclosing   lagoons   and  tide    marshes.      Farther  north  at 


SHORE  LINES 


809 


Long  Branch,  a  noted  seaside  resort,  the  land  is  already 
cut  back  in  a  low  bluff.  Severe  storms  cut  away  the  base 
of  the  bluff,  sometimes  undermining  the  houses  that  are 
built  too  close  to  it. 

The  low  coast  of  the  middle  Netherlands  has  retreated 
two  miles  or  more  in  historic  times.  A  belt  of  dunes, 
half  a  mile  or  more  wide,  lies  inland  from  the  smootli 


^^^^^^^^^ 

^^^^^^^==^~- 

^^^^g 

^^^^^^^^^^^ 

^^^^^^^^^ 

^^^g 

^^^^^^^^^B 

^^^^^^^^^^^ 

=S==: 

^^^^^ 

^ 

FiQ.  159.    Diagram  of  a  Lowland  Coast  with  Bluff  and  Sand  Reef 

Draw  an  outline  map  illustrating  the  features  of  Figure  159. 
Draw  another  map  representing  an  earlier  stage  in  the  development 
of  this  shore  line,  when  the  whole  length  of  shore  was  fronted  by  a 
reef  and  before  any  blufE  had  been  cut.  Draw  a  third  outline  show- 
ing a  later  stage,  when  the  retreat  is  great  enough  to  produce  a  bluff 
nearly  all  along  the  shore  line,  leaving  only  a  small  part  fronted 
with  sand  reef  and  marsh-filled  lagoon. 

harborless  beach.  The  chief  ports  are  on  the  lower 
courses  of  rivers,  whose  channels  are  broadened  by  the 
flow  and  ebb  of  the  tides. 

The  Romans  built  a  castle  back  of  the  dunes,  near  the 
mouth  of  the  Rhine.  In  1520  the  dunes  had  blown 
inland,  grain  by  grain,  and  the  sea  had  cut  the  shore  back 
close  to  the  castle.     In  1694  the  castle  stood  in  the  sea. 


310     ELEMENTARY  PHYSICAL  GEOGRAPHY 

about  half  a  mile  from  land.  In  1752  it  disappeared, 
destroyed  by  the  waves. 

In  1460  a  church  that  had  been  built  inside  the  dunes 
in  the  Dutch  village  of  Scheveningen  (near  The  Hague) 
was  reached  by  the  sea.  A  new  church  was  then  built 
about  a  mile  inland,  at  the  east  end  of  the  village.  In 
1574,  the  outer  part  of  the  village  having  been  gradu- 
ally consumed  by  the  waves,  new  houses  had  been  built 
east  of  the  church,  so  that  it  stood  in  the  middle  of  the 
village.  In  a  later  century  the  new  church  again  stood 
close  to  the  shore,  the  village  having  moved  beyond  it. 

In  southwestern  France  the  west  winds,  sweeping  in 
from  the  Bay  of  Biscay,  have  formed  a  belt  of  dunes  two 
or  three  miles  wide.  Formerly  the  sand  was  drifted  far- 
ther and  farther  inland  with  every  westerly  gale.  Fields 
and  villages  were  invaded  and  buried  by  the  advancing 
drifts.  Now  most  of  the  dunes  have  been  planted  with  a 
kind  of  pine  tree  that  thrives  in  a  sandy  soil ;  the  wind  is 
lifted  from  the  sand  by  the  trees,  and  the  sand  drifts  have 
ceased  advancing.     The  pine  forests  yield  much  resin. 

179.  Sea  Cliffs.  —  As  the  margin  of  a  plain  is  cut  back 
by  the  sea,  the  shore  bluff  increases  in  length  and  height, 
until  it  may  deserve  the  name  of  cliff.  The  cliff  face 
weathers ;  fragments,  large  and  small,  fall  from  it  to  the 
beach  below,  where  they  are  moved  about  and  ground  to 
pieces,  by  the  waves.  The  fine  particles  are  drifted  off- 
shore to  deeper  water.  Thus  longer  and  longer  stretches 
of  the  shore  become  harborless,  and  traffic  between  land 
and  sea  is  greatly  hampered. 


SHORE  LINES 


311 


In  northwestern  France  the  upland  plain  of  Normandy- 
fronts  the  sea  in  a  vertical  sea  cliff,  200  or  300  feet  high, 
with  gently  curving  shore  line  for  many  miles.  A  large 
part  of  the  plain  must  have  been  consumed  by  the  sea  in 
the  development  of  the  cliff. 


Fig.  160.    The  Sea  Cliffs  of  Normandy  (looking  southwest) 

180.  Shore  Lines  of  the  Second  Kind.  —  These  shore 
lines  are  more  varied  than  those  thus  far  described.  When 
an  uneven  land  surface  is  depressed  and  partly  covered  by 
the  sea,  numerous  ridges  and  hills  stand  forth  as  promon- 
tories and  continental  islands,  valleys  are  entered  by  arms 
of  the  sea,  and  protected  harbors  are  plentiful.  The  irreg- 
ular coast  of  Maine  offers  many  illustrations  of  this  kind. 
Its  relief  is  of  moderate  measure. 

The  waves  beat  furiously  on  the  exposed  headlands  of 
irregular  coasts  during  storms.     Angular  rock  fragments, 


312 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


weathered  from  the  rocky  coast,  are  swept  about  by  the 
dashing  waves  and  are  in  time  rounded  to  cobbles  and 

pebbles,  and 
worn  down  to 
sand.  These 
fragments  bat- 
ter the  shore 
and  erode  the 
margin  of  the 
land,  gradually 
forming  a  cliff 
that  rises  above 


Fig.  IGl.    Diagram  of  an  Irregular  Shore  Line 


sea  level  and  a  bench  that  is  partly  bare  at  low  tide. 

Isolated  rock  columns  or  stacks  stand  for  a  time  on  the 
rock  bench.  At  high  tide  the  waves  roll  across  the  bench 
and  sometimes 
excavate  sea 
caves,  fifty  or 
more  feet  in 
length,  at  the 
base  of  the  cliff. 
Fingal's  cave, 
on  the  island 
of  Staffa,  west 
of  Scotland, 
and  many  other 
less  famous  caves  have  thus  been  eroded  by  the  waves. 

As  the  wave-cut  bench  broadens  and  the  cliffs  increase 
in  height,  some  of  the  rock  waste  is  swept  alongshore 
from  the  headlands  into  the  little  coves  and  bays,  forming 


Fig.  162.    Diagram  of  an  Irregujar  Shore  Line  with 
Cliff ed  Headlands  and  Beached  Bays 


SHORE  LINES 


313 


beaches  on  the  more  protected  parts  of  the  coast  line. 
Such  beaches  present  a  smooth  curve,  concave  to  the 
sea ;  here  the  surf  breaks  in  even  rollers,  quite  unlike  the 
dashing  and  fretting  waves  on  the  ragged  headlands. 

Draw  maps  of  selected  parts  of  the  coast  shown  in  Figures  161 
and  162,  on  a  somewhat  larger  scale  than  that  of  the  figures,  and 
thus  illustrate  the  change  from  the  original  to  the  later  outline. 

The  cobbles  and  pebbles  thrown  up  on  the  beaches  dur- 
ing storms  may  form  a  wall  five  or  ten  feet  above  high 
tide.  A  pond  or 
swamp  is  often 
inclosed  behind 
the  wall  beach 
in  the  valley 
that  had  previ- 
ously opened 
into  the  bay. 
The  New  Eng- 

Fig.  163.    Diagram  of  a  Curved  Shore  Line 

land  coast  has 

numerous  beaches  of  this  kind  between  its  rocky  headlands. 

Compare  the  coast  forms  in  Figures  161,  162,  and  163.  Where 
has  the  sea  gained  on  the  land  ?  the  land  on  the  sea  ? 

The  promontory  of  Brittany  in  western  France,  beaten 
by  heavy  waves  and  swept  by  strong  tides,  is  in  about  the 
stage  of  development  represented  by  Figure  162.  The 
headlands  are  dangerous  on  account  of  the  rocky  reefs 
that  rise  to  half-tide  height  on  the  rock  bench  that  fronts 
the  ragged  cliffs.  The  small  bays  are  partly  filled  with 
curved  beaches  of  cobbles,  pebbles,  and  sand. 


314  ELEMENTARY  PHYSICAL  GEOGRAPHY 

As  time  passes,  headlands  are  cut  farther  back,  so  that 
the  cliffs  become  higher  and  longer.  The  bays  are  more 
and  more  filled  with  beaches  and  cobbles,  gravel  and  sand, 
and  with  deltas  formed  by  streams  entering  the  bay  heads. 
Thus  the  outline  of  the  shore  becomes  more  regularly 
curved  than  it  was  at  first,  and  convex  lines  of  cliffs 
alternate  with  concave  stretches  of  beach. 

Fine  examples  of  shores  in  this  stage  are  found  in 
parts   of  southwestern  England.     The  cliffed  headlands 


Fig.  1G4.     A  Cliffed  Headland  and  a  Land-Tied  Island 

are  guarded  by  lighthouses ;  settlements  are  usually  found 
in  the  river  mouths  of  the  beached  bays.  The  coast  of 
western  Italy  and  the  northern  coast  of  California  offer 
many  examples  of  this  kind. 

181.  Land-Tied  and  Sea-Cut  Islands.  —  Irregular  coasts, 
formed  by  the  depression  of  a  mountainous  region,^  are 
often  originally  fronted  by  islands.  Such  islands  not  infre- 
quently come  to  be  attached  to  the  mainland  by  the  back- 
ward growth  of  sand  reefs  that  are  supplied  with  waste 
from  the   outer  cliffs.     Compare  the  two  headlands   of 


SHORE  LINES 


315 


Figure  164  in  this  respect.  A  land 
of  Italy  is  shown  in  Plate  XVI. 

The  fortified  Rock  of  Gibraltar, 
belonging  to  Great  Britain,  was 
originally  an  island,  but  is  now 
tied  to  the  mainland  of  Spain  by 
a  broad  sand  reef.  Part  of  the 
reef  is  "neutral  ground,"  occu- 
pied by  neither  Spain  nor  Great 
Britain. 

If  the  coast  is  of  unequal 
strength  along  its  front,  the  rate 
of  sea  cutting  may  vary  from 
place  to  place,  and  thus  parts  of 
the  coast  may  in  time  be  cut  off 
from  the  mainland  and  form 
islands,  as  in  Figure  166.  Many 
islands  in  the  bay  of  Panama  are 
thus  formed.    They  are  remnants 


-tied  island  on  the  coast 


Europa  Poinl- 


Fig.  1G5.    Gibraltar 


Fig.  1G6.    Diagram  of  a  Group  of  Sea-Cut  Islands 


316 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


of  the  mainland  whose  extent  has  been  much  reduced  by 
the  attack  of  the  sea.  The  width  of  the  isthmus  of 
Panama  has  thus  been  lessened  and  the  length  of  the  pro- 
posed interoceanic  canal  across  it  has  been  correspondingly- 
shortened. 


Fig.  167.    A  Cliffed  Coast  in  Alaska 


182.  Cliffed  Coasts.  —  Coasts  that  have  been  long 
exposed  to  strong  waves  and  tides  may  have  been  cut  so 
far  back  that  no  part  of  the  original  outline  remains.  In 
such  cases  a  nearly  continuous  cliff,  sometimes'  of  great 
height,  fronts  the  shore,  as  in  Figure  167.     Traffic  between 


SHORE  LINES 


317 


land  and  sea  is  practically  impossible  on  such  a  coast.  A 
vessel  wrecked  on  the  ragged  bench  beneath  the  cliffs  can 
receive  little  succor  while  stormy  weather  lasts. 

The  Orkney  and  Shetland  islands,  north  of  Scotland, 
have  lost  much  of  their  former  area  by  the  attack  of  the 
sea.  The  head- 
lands are  cut  off 
by  lofty  cliffs, 
some  of  which  are 
nearly  1000  feet 
high.  An  isolated 
stack,  known  as 
the  "Old  Man  of 
Hoy,"  rises  600 
feet  above  the  sea. 

183.  Elevated 
Shore  Lines. — 
When  the  devel- 
opment of  shore 
lines  is  interrupt- 
ed by  a  change  in 
the  level  of  the 
land,  the  work  of 
cliff  cutting  and  bay  filling  must  be  begun  again  at  a 
new  level,  in  much  the  same  way  as  before. 

If  the  land  rises,  the  former  shore  line  may  be  found 
at  a  greater  or  less  distance  inland  from  the  new  shore 
line.  This  has  already  been  referred  to  in  the  descrip- 
tion of  coastal  plains. 


Fig.  1G8.    Ihe  ' '  Old  Man  of  Hoy ' 


318  ELEMENTARY  PHYSICAL  GEOGRAPHY 

An  elevated  shore  line,  marked  chiefly  by  rocky  cliffs  and 
benches  with  occasional  beaches,  may  be  traced  along  a 
great  part  of  the  western  coast  of  Scotland  at  a  height  of 
from  twenty  to  twenty-five  feet  above  the  sea  level  of  to-day. 
The  narrow  coastal  plain  that  slopes  forward  from  the  old 
shore  line  to  the  new  one  is  pictured  in  Figure  64.  This 
elevated  shore  line  forms  a  convenient  bench  along  which 
roads  may  be  laid  near  the  base  of  the  slopes  that  ascend 
to  the  highland  summits.  Old  sea  caves,  roughly  walled 
in,  sometimes  serve  as  stables  for  the  seaside  farmers. 

A  low  bluff,  seeming  to  be  a  former  shore  line,  has 
been  traced  on  the  coastal  plain  of  Virginia  and  North 
Carolina,  a  short  distance  inland  from  the  present  shore 
line.  Lines  of  ancient  sea  cliffs  at  several  different 
levels  break  the  coastal  slopes  of  Cuba  and  form  steps 
in  the  broad  plains  of  eastern  Patagonia. 

The  western  coast  of  Norway  is  bordered  for  much  of  its 
length  by  a  belt  of  lowland  and  islands,  sometimes  as 
much  as  from  three  to  ten  miles  wide,  from  whose  inner 
margin  an  old  sea  cliff  rises  to  the  highlands  (Figure  169). 
The  lowland  is  a  broad  rock  bench  or  platform,  cut  by  the 
sea  when  the  land  stood  about  300  feet  lower  than  now. 
A  large  part  of  the  population  of  western  Norway  dwells 
on  this  ancient  sea  floor. 

The  former  sea  cliff,  at  the  inner  margin  of  the  plat- 
form, is  from  500  to  1000  feet  high.  A  number  of 
rocky  hills  stand  on  the  platform,  representing  uncon- 
sumed  islands  of  the  former  shore. 

The  withdrawal  of  lake  waters  by  a  change  of  climate 
(page  288)  has  an  effect  on  the  condition  of  shore  lines 


SHORE  LINES 


319 


similar  to  that  produced  by  an  elevation  of  the  land  with 
respect  to  the  sea.  The  cliffs  and  beaches  that  contour 
around  the  slopes  of  the  mountains  of  Utah,  where  the 
waves  of  Lake  Bonneville  once  beat,  in  many  ways 
resemble  the  elevated  shore  lines  of  western  Scotland. 

Well-defined  ancient  shore  lines,  consisting  of  cliffs  and 
beaches,  are  found  in  the  region  of  the  Great  lakes.     The 


Fig.  169.    The  Coast  Platform  of  Norway 

shore  lines  are  found  to  converge  toward  depressions  in  the 
height  of  land  to  the  south  of  the  lakes,  and  well-defined 
channels  are  there  discovered.  This  indicates  the  former 
existence  of  lakes  much  larger  and  deeper  than  those 
of  to-day,  with  outlets  southwestward  to  the  Mississippi 
system,  instead  of  northeastward  by  the  St.  Lawrence. 

These  facts  are  explained  by  supposing  that  the 
melting  ice  sheet  of  the  glacial  period  obstructed  the 
St.  Lawrence  valley,  so  that  the  lake  waters  had  to  rise 


320  ELEMENTARY  PHYSICAL  GEOGRAPHY 

high  enough  to  overflow  southwestward.  Many  of  the 
beaches  are  so  distinct  that  they  are  used  as  naturally 
graded  roadways.  The  outlet  of  the  expanded  Lake 
Erie  ran  past  the  site  of  Fort  Wayne,  Indiana,  to  the 
Wabash  river.  The  outlet  of  the  expanded  Lake 
Michigan  led  past  the  site  of  Chicago  to  the  Illinois 
river;  this  channel  is  now  followed  by  the  artificial 
drainage  canal  by  which  some  of  the  water  of  Lake 
Michigan  is  again  led  along  the  line  of  ancient  outlet. 

184.  Fiords.  —  The  valleys  in  the  highlands  of  Norway 
have  been  deepened  by  the  heavy  and  strong-moving  glaciers 
that  once  filled  them.  Since  the  glaciers  disappeared  the 
sea  has  entered  the  deep  channels  that  the  ice  scoured  out, 
forming  long,  narrow,  and  deep  embayments,  called  fiords^ 
often  deeper  at  the  middle  than  near  the  mouth.  Their 
depth  has  probably  been  increased  by  a  depression  of  the 
region,  by  which  the  border  of  the  ice-scoured  lowland  has 
been  converted  into  a  swarm  of  islands. 

The  rock  walls  of  the  fiords  are  so  steep  that  few  set- 
tlements can  be  made  along  them,  except  at  their  heads 
or  where  deltas  are  built  by  side  streams  that  cascade 
from  the  hanging  valleys  (see  page  299)  of  the  high- 
lands. Roads  can  seldom  follow  the  shore  lines;  hence 
communication  is  chiefly  by  water. 

An  irregular  coast  of  this  kind  has  often  favored  the 
development  of  maritime  arts.  Its  outlying  islands  tempt 
exploration*  its  protected  bays  afford  safe  harborage  even 
for  small  boats.  The  people  occupying  the  coastal  lands 
become  expert  sailors  and  fishermen. 


c 


SHORE  LINES  321 

The  numerous  bays  of  southern  Scandinavia  were  known 
as  viks  to  the  people  who  occupied  them  1000  years  ago, 
and  the  inhabitants  were  therefore  called  vikings^  or  bay 
people.     They  became  bold  marauders,  invading  the  more 

snn thorn  coasts  of  wostorn  Europe,  by  whose  people  the 


Fig.  170.     A.  Delta  in  a  Norwcgiuu  Fiord 

vikings  were  called  Northmen.  Normandy  is  to  this  day 
named  after  these  early  sea  kings.  They  were  the  first 
European  people  to  venture  far  out  upon  the  ocean,  and 
thus  almost  1000  years  ago  they  discovered  Greenland 
and  other  parts  of  the  western  world. 

The  west  coast  of  Patagonia  (southern  Chile)  resembles 
that  of  Norway  in  the  possession  of  deep  fiords  among 
bold   mountains.     The    Canoe    Indians   dwell   here,  —  a 


322     ELEMENTARY  PHYSICAL  GEOGRAPHY 

primitive  people  who  find  the  steep  slopes  of  the  land 
so  inhospitable  that  they  live  almost  entirely  in  open 
canoes  on  the  water.  A  small  fire  is  kept  burning  on  a 
few  sods  in  the  canoes,  so  that  it  may  be  carried  from 
place  to  place.  These  Indians  have  no  fixed  habita- 
tions and  make  little  use  of  the  land,  except  when 
they  build  temporary  shelters  of  tree  branches,  roughly 
thatched,  in  one  cove  or  another  where  they  stop  for  a 
time  to  gather  shellfish. 

The  mountainous  coast  of  'Alaska  is  varied  by  numer- 
ous fiords,  into  some  of  which  great  glaciers  descend  from 
snowy  ranges  in  the  background.  As  in  Norway,  much 
of  the  coast  is  so  steep  as  to  be  unfit  for  settlement. 
Hanging  valleys  frequently  open  on  the  walls  of  the  fiords, 
500  or  more  feet  above  sea  level. 

185.  Delta  Shore  Lines.  —  Rivers  tend  to  build  their 
deltas  forward,  and  thus  oppose  the  destructive  action  of 
the  sea.  The  Mississippi  discharges  a  great  quantity  of 
land  waste  into  the  Gulf  of  Mexico.  The  waters  of  the 
gulf  are  relatively  shallow,  and  the  tides  are  weak.  Here 
the  outline  of  the  delta  seems  to  be  governed  entirely  by 
the  action  of  the  great  river  (Figure  136). 

The  several  distributaries  of  the  Mississippi  build  low 
and  slender  banks  of  mud  on  each  side  of  their  channels 
faster  than  the  waves  can  wear  them  away;  hence  the 
delta  has  several  fingerlike  projections  into  the  sea.  In 
order  to  increase  the  depth  of  water  in  one  of  the  channels, 
or  "passes,"  jetties  (dikes  of  wood  and  stone)  have  been 
built  forward  beyond  the  end  of  the  delta  fingers,  thus 


SHORE  LINES 


323 


increasing  the  current  and  forcing  it  to  scour  the  channel 
to  a  depth  sufficient  for  seagoing  vessels  to  enter  on  their 
way  to  New  Orleans. 

The  Rio  Grande,  a  large  river,  but  much  smaller  than 
the  Mississippi,  delivers  land  waste  to  the  gulf  in  greater 
quantity  than  the  waves 
and  currents  can  altogether 
remove;  hence  its  delta  is 
built  forward  (Figure  171). 
But  the  waves  are  strong 
enough  to  smooth  the  out- 
line of  the  delta;  hence  it 
has  a  gently  convex  curve 
without  fingerlike  projec- 
tions. The  Brazos  and  Col- 
orado rivers,  about  midway 
between  the  Mississippi  and 
the  Rio  Grande,  also  cause 
a    slight    forward    bowing 

of   the    Texas    coast.  Fig.  171.    Deltas  of  the  Texas  Coast 


186.  Effect  of  Climate  on  Shore  Lines.  —  Shore  lines, 
like  land  forms,  are  affected  by  climate ;  not  only  by 
differences  between  regions  of  onshore  and  offshore  winds, 
where  waves  and  currents  are  stronger  or  weaker,  but  even 
more  by  differences  of  temperature. 

In  polar  seas  the  land  is  often  bordered  by  a  fringe  of 
ice  called  the  ice  foot.  During  the  winter  the  ice  foot 
usually  remains  attached  to  the  land,  unless  broken  by 
strong  tides ;   in  summer  it  may  loosen  and  float  away. 


324 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


It  is  often  used  as  a  longshore  roadway  for  sled  travel  by 

Eskimos  and  Arctic  explorers. 

In  warm  seas  the  shores  that  are  not  exposed  to  strong 

surf  may  be  invaded  by  certain  kinds  of  trees,  forming  a 

network  so  dense  as  to  make  landing  difficult. 

The  mangrove  is  the  most  important  tree  of  this  kind. 

It  grows  freely  in 
shallow  sea  water 
on  low  and  muddy 
shores,  and  protects 
the  land  from  the 
waves.  Muddy  sedi- 
ments accumulate 
in  the  quiet  water 
among  the  trees,  and 
thus  the  land  gains 
on  the  sea.  Shores 
;dl  overgrown  with 

Fig.  172.    Mangrove  Tree  mangrove       SWamps 

are  dismal  as  com- 
pared with  the  clean  shell-strewn  beaches  of  sand  and 
pebbles  beaten  by  trade-wind  surf. 


187.  Coral  Reefs.  —  The  shallow  waters  of  continental 
borders  or  mid-ocean  islands  in  the  warmer  seas  are 
commonly  occupied  by  coral  reefs,  composed  of  the 
limy  framework  of  coral  animals.  Living  corals  are 
found  chiefly  on  the  outer  side  of  the  reef,  where  they 
grow  in  the  shallow  water  much  in  the  same  way  that  a 
thicket  of  small  bushes  grows  on  the  land.     They  take 


SHORE  LINES 


325 


Fig.  173.    A  Fringing  Reef 


the  limestone  needed  for  their  skeletons  from  solution  in 
the  sea  water. 

When  reef-building  corals  first  take  possession  of  the 
shallow  waters  on  a  shoal  or  near  a  shore  line,  their  growth 
extends  upward  from 
the  shallow  bottom  and 
outward  into  the  surf. 
Blocks  and  branches  are 
detached  from  the  bot- 
tom by  severe  storms 
and  rolled  about  by  the  waves ;  the  larger  fragments  are 
thrown  together,  forming  a  beach  a  little  above  sea  level ; 
the  finer  particles  are  carried  toward  deep  water  and  strewn 
over  the  sloping  bottom.  The  reef  thus  broadens,  and  if 
near  the  land,  it  forms  a  fringe  close  along  the  shore  line. 
At  this  stage  it  is  called  a  fringing  reef. 

Strips  of  fringing  reef  are  found  on  the  equatorial  coast 
of  eastern  Africa,  along  parts  of  the  Brazilian  coast,  at 
various  points  on  the  coast  of  Cuba  and  elsewhere  in  the 

West  Indies,  and  border- 
ing many  islands  in  the 
Pacific,  as  the  Hawaiian 
and  other  groups.  The 
Galapagos  islands  in  the 
eastern  Pacific,  close  to 
the  equator,  are  free  from  reefs,  because  of  the  low  tem- 
perature of  the  water  brought  there  by  the  strong  Peruvian 
current.     (See  Figure  112.) 

Draw  maps  of  the  islands  and  reefs  shown  in  Figures  173  and 
174.     Compare  the  two. 


Fig.  174.    A  Barrier  Reef 


326 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


FiQ.  175.    Part  of  the  Great  Barrier  Reef  of  Australia  (as  seen  at  low  tide, 
looking  toward  the  mainland) 

188.  Barrier  Reefs.  —  A  fringing  reef  broadens  by  the 
outward  growth  of  the  corals,  and  the  submarine  slope  is 
built  forward  by.  the  supply  of  coral  fragments.  At  the 
same  time  water  supplied  by  rain,  by  streams  from  the  land, 


SHORE  LINES 


327 


Fig.  176.    Diagram  of  Part  of  a 
Barrier  Reef 


and  especially  by  the  surf  that  rolls  over  the  reef,  slowly  dis- 
solves and  washes  away  the  inner  part  of  the  reef  where  liv- 
ing corals  are  few  or  wanting.  Thus  the  reef  may  come  to  be 
separated  from  the  land 
by  a  shallow  lagoon  a 
mile  or  more  wide ;  and 
in  this  way  a  fringing 
reef  may  change  to  a 
barrier  reef. 

The  Great  Barrier  reef 
stretches  along  the  north- 
east coast  of  Australia 
for   about   1000    miles, 

the  largest  reef  in  the  world.  It  is  usually  from  twenty 
to  fifty  miles  from  the  mainland,  mostly  beneath  sea  level, 
interrupted  by  numerous  inlets,  and  bearing  a  few  low 

islets.  The  sea  outside 
descends  rapidly  to  great 
depths ;  the  water  inside 
is  shallow  (from  ten  to 
forty  fathoms). 

189.    Effects  of  Eleva- 
.     „,        ,    tion.  ^If  a  slow  uplift 

Fig.  177.    Diagram  of  Part  of  an  Elevated  .       ^ 

Reef  with  a  New  Fringing  Reef  OCCUrs,  COrals  will   con- 

tinue to  grow  on  the 
outer  face  of  the  reef,  but  the  body  of  the  reef  may  be 
raised  above  sea  level,  forming  a  terracelike  bench  above 
the  new  shore  line,  outside  of  which  new  fringing  reefs 
grow.     Compare  Figures  176  and  177. 


328 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


An  uplifted  reef,  forming  a  bench  at  a  height  of  about 
thirty  feet,  with  a  breadth  of  a  mile  or  less,  borders  much 
of  the  northern  coast  of  Cuba.  The  sea  has  worn  a  low 
cliff  in  the  front  of  the  bench ;  from  the  cliff  top  one  may. 
look  down  upon  the  new  fringing  reef  now  growing  in 
the  sea. 

The  loose  texture  of  uplifted  reefs  allows  them  to  be 
worn  down  again  with  relative  rapidity.  While  the 
uplifted  reef  is  thus  wasting  away,  the  fringing  reef  may 
be  growing  outward  vigorously  and  changing  to  a  barrier 
reef.  The  uplifted  reef  will  be  in  part  dissolved  by  the 
solvent  action  of  rain  water;  and  it  may,  after  elevation 
ceases,  be  reduced  below  sea  level.  A  shallow  body  of 
water,  or  lagoon,  will  thus  be  formed  within  the  new 
barrier  reef. 

190.   Atolls.  —  If  the  central  island  within  a  barrier  or 

fringing  reef  is  worn  away  or  is  lost  by  slow  submergence 

as  the  reef  grows  upward 
and  outward,  the  reef  may 
make  an  irregular  ring 
around  an  oval  lagoon 
and  the  ring  may  slowly 
increase  in  size  by  the 
outward    growth    of   the 

reef,  while  the  lagoon  is  deepened  by  the  dissolving  action 

of  its  waters. 

Such  a  ring  island  is  called  an  atoll.     Many  islands  of 

this  kind  are  known  in  the  Pacific  ocean. 


Fig.  178.    Diagram  of  an  Atoll 


Compare  the  reefs  shown  in  Figures  173,  174,  and  178. 


SHORE  LINES 


329 


Although  one  of  the  most  wonderful  objects  in  nature, 
a  lonely  atoll  affords  little  opportunity  for  human  devel- 
opment. The  natives  of  such  islands  lead  easy  and  indo- 
lent lives,  but  their  progress  toward  better  conditions  than 
those  of  savagery  is  hindered  by  the  small  variety  in  their 
surroundings  and  by  their  distance  from  lands  of  more 
varied  form  and  products. 


i'"iG.  17'J.     An  AloU,  or  Coral  Island 


The  small  height  of  atolls  subjects  them  to  the  danger 
of  being  overwhelmed  by  earthquake  waves.  Hurricanes 
sometimes  come  upon  them,  unobstructed  from  the  open 
sea,  sweeping  violent  surf  far  up  the  beaches;  the  storm 
winds  break  down  the  cocoanut  palms  on  which  the 
natives  depend  largely  for  food  and  for  the  materials  for 
many  of  their  simple  arts.  Atolls  have  no  streams,  but 
fresh  water  supplied  by  rains  may  be  found  not  far  below 
the  surface.     The  thin  soil  has  little  variety  of  mineral 


3B0  ELEMENTARY  PHYSICAL  GEOGRAPHY 

matter,  but  floating  pumice  (frothy  lava)  is  often  cast 
ashore  from  distant  volcanic  eruptions,  and  some  of  the 
islanders  have  learned  to  gather  and  pulverize  it  to  use 
as  a  fertilizer  for  their  little  fields.  Floating  logs  from 
other  lands  sometimes  drift  upon  the  atolls,  and  their 
roots  occasionally  carry  stones  of  firmer  texture  than 
coral  rock  (for  example,  fragments  of  dense  lava  from 
a  volcanic  island) ;  rude  whetstones,  pestles,  and  mortars 
are  made  from  these  chance  supplies. 

Although  birds  are  plentiful,  there  were  no  mammals 
on  coral  islands  until  rats  and  mice  came  ashore  from 
vessels;  a  few  domestic  quadrupeds  have  occasionally 
been  imported  by  foreign  residents.. 

QUESTIONS 

Sec.  175.  What  is  the  origin  of  the  forces  by  which  the  ocean 
works  on  the  lands?  How  is  the  work  done?  What  becomes 
of  the  material  worn  away?  Why  are  the  lands  not  completely 
worn  away? 

176,  177.  Upon  what  two  conditions  does  the  outline  of  any  shore 
line  depend  ?  Describe  the  movement  of  waves  and  their  action  on  the 
lands.  How  are  shore  currents  caused  ?  How  do  waves  aid  the  work 
of  currents?  Compare  the  work  of  the  sea  in  deep  and  in  shallow 
shore  waters.  Describe  the  shore  line  of  a  young  coastal  plain ;  of 
a  depressed  mountain  range.  Contrast  them  as  to  harbors,  settle- 
ment, and  trade. 

178.  Describe  the  shore  of  the  coastal  plain  of  Buenos  Aires. 
What  effects  are  here  caused  by  storm  winds?  by  waves?  What 
are  the  origin  and  form  of  sand  reefs  ?  What  are  inlets  ?  lagoons  ? 
salt  marshes  ?  How  are  the  sand  reefs  and  lagoons  changed  by  the 
action  of  surf  ?  Describe  the  coast  of  New  Jersey ;  of  the  Nether- 
lands ;  of  southwestern  France. 


SHORE  LINES  331 

179.  What  is  the  origin  of  sea  cliffs  ?  How  are  they  worn  back  ? 
Describe  the  cliffed  coast  of  northwestern  France. 

180.  What  are  the  features  of  a  shore  line  of  the  second  class  ? 
How  and  on  what  parts  of  these  shores  do  waves  form  cliffs? 
stacks?  caves?  beaches?  What  are  wall  beaches  and  where  are 
they  common?  Describe  the  coast  of  Brittany.  Describe  the  shore 
forms  of  later  development.     Where  are  they  found  ? 

•  181,  182.  What  are  land-tied  islands?  Describe  an  example. 
What  are  sea-cut  islands?  Describe  some  examples.  Describe  a 
cliffed  coast.  What  is  the  relation  of  such  a  coast  to  human  occu- 
pation ?     Describe  an  example.     What  is  the  "  Old  Man  of  Hoy  "  ? 

183.  What  changes  in  the  shore  line  result  from  a  change  in  the 
level  of  the  land  ?  Describe  the  elevated  shore  line  of  western  Scot- 
land; of  North  Carolina.  Where  are  other  examples  found  ?  Describe 
the  western  coast  of  Norway.  Under  what  conditions  were  certain 
abandoned  shore  lines  formed  in  Utah  ?  around  the  Great  lakes  ? 

184.  What  are  fiords?  Explain  their  origin.  Where  do  they 
occur?  How  do  they  affect  settlements?  How  does  an  irregular 
shore  line  affect  the  maritime  arts  ?  Give  an  example  from  Scandi- 
navia. Describe  the  Canoe  Indians.  What  is  the  relation  of  hang- 
ing valleys  to  fiords  ? 

185.  How  do  rivers  tend  to  oppose  the  action  of  the  sea? 
Describe  the  delta  of  the  Mississippi ;  of  the  Rio  Grande. 

186.  How  does  climate  affect  shore  lines?  What  is  the  ice  foot? 
Describe  a  mangrove  swamp.     Where  is  such  a  swamp  formed  ? 

187.  188.  What  are  coral  reefs  ?  Where  are  they  found  ?  (See 
Figure  112.)  How  are  they  formed?  What  is  a  fringing  reef? 
Where  are  fringing  reefs  found  ?  Why  are  no  reefs  found  on  the 
Galapagos  islands?  What  is  a  barrier  reef?  How  is  it  formed? 
Describe  the  Great  Barrier  reef  of  Australia. 

189,  190.  Describe  an  uplifted  reef.  What  changes  may  such  a 
reef  undergo?  What  is  an  atoll?  In  what  ways  may  atolls  be 
formed?  What  opportunity  do  atolls  afford  for  human  develop- 
ment ?     To  what  danger  are  atolls  exposed  ? 


CHAPTER  XI 
THE  DISTRIBUTION  OF  PLANTS,  ANIMALS,  AND  MAN 

191.  Geographical  Aid  in  Human  Progress.  —  The  study 
of  physical  geography,  or  physiography,  gives  a  knowl- 
edge of  the  features  of  the  earth,  so  that  we  may  better 
understand  the  relation  of  man  and  nature.  This  rela- 
tion is  of  great  importance,  because  the  progress  of  man- 
kind from  the  savage  toward  the  civilized  state  has  been 
largely  made  by  taking  advantage  of  favorable  geograph- 
ical conditions  and  by  learning  to  make  greater  and  better 
use  of  the  products  and  forces  of  the  earth. 

The  winds  blew  over  the  lands  and  waters,  carrying 
rain  and  causing  waves  and  currents,  for  thousands  of 
years  while  man  was  an  ignorant  savage.  When  he 
invented  sailboats  and  windmills  a  new  use  was  made 
of  the  winds,  and  man  profited  greatly  by  his  inventions. 
Streams  had  been  wearing  down  the  falls  and  rapids  in 
their  valleys  and  spreading  rock  waste  over  their  flood 
plains  during  all  the  long  existence  of  the  continents. 
When  man  cultivated  food-bearing  plants  on  the  flood 
plains  and  built  flour  mills  by  the  waterfalls,  he  gained 
much  from  making  new  and  good  use  of  these  natural 
forms  and  forces. 

The  magnetic  forces  of  the  earth  have  always  been  capa- 
ble of  directing  a  compass  needle,  but  they  were  hot  used 

332 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        333 

until  man  discovered  how  a  balanced  magnetized  needle 
would  behave.  Coal  and  iron  ore  lay  untouched  in  the 
earth's  crust  for  millions  of  years ;  now  the  nations  that 
make  the  fullest  use  of  these  invaluable  resources  have 
become  the  leaders  of  the  world. 

Reference  has  frequently  been  made  on  the  earlier  pages 
of  this  book  to  the  effects  of  geographical  surroundings 
on  the  growth  and  distribution  of  plants  and  animals  and 
on  man's  way*of  living.  The  present  chapter  reviews 
these  effects  and  gives  new  examples  of  them. 

192.  Life  on  the  Earth.  —  The  earth  is  known  to  have 
been  occupied  for  ages  past  by  various  kinds  of  plants 
and  animals,  for  their  fossil  remains  are  found  in  many 
rock  layers  of  ancient  origin.  During  all  these  ages 
living  forms  have  tended  to  spread  over  as  large  a 
region  as  possible,  just  as  they  do  now. 

Barriers  of  different  kinds  limit  the  spreading  of 
organic  forms.  Land  plants  and  animals  are  stopped  by 
the  sea,  unless  they  can  travel  by  water  or  air.  Sea 
animals  are  stopped  by  the  lands.  Those  forms  that 
need  a  warm  climate  do  not  spread  into  regions  of  cold 
climate.  Grazing  animals  that  need  abundant  grass  are 
stopped  by  deserts  and  by  forested  mountains. 

Plants  growing  from  heavy  seeds,  like  nuts,  spread 
slowly  from  the  parent  plant.  Plants  growing  from 
light  seeds,  especially  from  such  as  are  carried  by  the 
wind, -like  the  seeds  of  the  dandelion,  the  thistle,  and 
the  fireweed,  are  very  rapidly  distributed.  The  dande- 
lion is  found  on  the  northern  lands  all  around  the  earth. 


334  ELEMENTARY  PHYSICAL  GEOGRAPHY 

Certain  kinds  of  sea  animals,  like  mussels,  barnacles, 
and  corals,  spend  most  of  their  life  attached  or  rooted 
to  the  sea  bottom,  living  on  food  that  is  brought  to 
them  by  the  moving  waves  and  currents.  This  reminds 
one  of  the  dependence  of  rooted  land  plants  on  the  mov- 
ing air  for  most  of  their  sustenance.  But  the  young 
forms  of  these  fixed  animals  are  free  to  float  about,  and 
are  then  carried  far  and  wide  by  the  currents  of  the  sea, 
just  as  light  seeds  are  carried  by  the  winds. 

Most  animals  can  move  from  place  to  place.  They  have 
fins  for  swimming,  legs  for  walking,  or  wings  for  flying.  As 
they  wander  about  in  search  of  food,  they  come  in  time  to 
be  distributed  over  all  parts  of  the  earth  accessible  and 
favorable  to  them.  This  is  as  true  for  the  ancient  history 
of  life  on  the  earth  as  it  is  for  the  life  of  to-day. 

Birds  of  strong  flight  are  widely  distributed.  Walking 
birds  and  quadrupeds  are  more  narrowly  limited.  The 
ostrich  of  Africa,  the  emu  of  Australia,  and  the  rhea  of 
South  America  are  each  confined  to  one  of  the  southern 
continents.  The  albatross,  a  large  sea  bird,  whose  skill 
in  flying  without  flapping  its  wings  is  very  remarkable, 
is  found- all  around  the  great  southern  oceans. 

Occasional  examples  of  some  fifty  kinds  of  North 
American  birds  are  found  in  western  Europe ;  but  no 
stragglers  from  Europe  are  found  in  North  America. 
This  is  because  the  prevailing  westerly  winds  blow  from 
North  America  toward  Europe.  The  course  of  the  winds 
is  determined  by  the  direction  of  the  earth's  rotation,  and 
thus  the  rotation  of  the  earth  has  an  influence  on  animal 
distribution. 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        335 

193.  Geographical  Factors  in  the  Struggle  for  Existence. 
—  The  number  of  plants  and  animals  in  a  given  region  is 
usually  about  as  great  as  can  be  supported  there.  Where 
food  is  plenty  the  number  of  individuals  is  large ;  this  is 
usually  the  case  in  the  shallow  borders  of  the  seas  and 
on  the  lands  of  the  temperate  and  torrid  zones.  The 
luxuriant  plant  growth  of  the  forests  under  the  equa- 
torial  rains  illustrates  this  rule.  Where  food  is  scarce, 
as  in  very  dry  and  in  very  cold  regions,  the  number  of 
individuals  is  small;  and  some  of  the  cold,  snow-covered 
deserts  are  almost  uninhabited,  as  in  central  Greenland. 

Man  frequently  causes  great  changes  in  the  numbers 
of  plants  and  animals,  as  when  he  cuts  down  the  trees 
of  a  forest  and  plants  grain  in  the  new-cleared  fields, 
or  when  he  kills  the  wild  animals  of  a  region  and  intro- 
duces domestic  animals  in  their  place.  But  apart  from 
changes  of  this  kind,  the  plants  and  animals  of  a  region 
remain  at  about  the  same  number  for  centuries. 

It  is,  however,  well  known  that  every  kind  of  plant 
and  animal  tends  to  increase  in  numbers,  for  the  seeds 
of  plants  and  the  offspring  of  animals  are  always  more 
numerous  than  the  individuals  that  produce  them.  A 
single  grain  of  corn  may  grow  to  a  stalk  bearing  several 
ears,  each  of  which  may  bear  over  a  hundred  grains. 
Many  thousand  eggs  are  contained  in  the  roe  of  a  single 
salmon.  If  all  the  young  plants  and  animals  reached 
maturity  and  produced  other  young  forms  in  their  turn, 
the  number  bi  individuals  would  increase  enormously. 

The  reason  that  the  number  of  plants  and  animals 
in  a  district  does  not  greatly  increase  is  that,  in  spite  of 


336  ELEMENTARY  PHYSICAL  GEOGRAPHY 

the  production  of  numerous  young  individuals,  many  of 
them  perish  in  the  severe  competition  for  an  opportimity 
to  live.  Many  seeds  fail  to  germinate  because  they  fall 
on  unfit  soil,  or  because  they  are  eaten  by  animals. 
Many  young  animals  are  devoured  by  other  animals. 
As  a  rule,  those  individuals  survive  which  have  some 
advantage  over  their  fellows  and  are  therefore  more  fit 
to  succeed  in  the  "  struggle  for  existence."  The  success 
of  these  individuals  is  often  called  the  "survival  of  the 
fittest";  and  the  survivors  are  said  to  be  chosen  from 
those  which  perish  by  "natural  selection." 

The  chances  of  survival  in  the  struggle  for  existence 
are  increased  for  those  plants  and  animals  which  are  best 
adapted  to  their  geographical  surroundings.  Fish  have 
gained  a  shape  that  enables  them  to  move  easily  through 
the  water ;  this  is  an  advantage  in  getting  their  food  and 
in  escaping  from  pursuit.  Many  of  the  smaller  animals 
of  the  open  ocean  move  slowly;  but  they  imitate  the 
transparence  of  sea  water  and  so  make  themselves  almost 
invisible  and  more  likely  to  escape  their  enemies. 

As  the  earth  is  lighted  from  the  sky,  many  animals 
whose  backs  are  dark  have  lighter  colors  underneath, 
so  as  to  counteract  the  effect  of  shade;  they  are  thus 
less  easily  seen  and  so  have  a  better  chance  of  approach 
to  their  prey  or  of  escape  from  their  enemies.  Animals 
inhabiting  deserts  are  usually  gray  or  tawny,  imitating 
the  color  of  the  bare  ground.  In  the  snow-covered 
Arctic  regions  many  animals  are  white. 

Some  animals  gain  protection  by  living  in  caverns  or 
in  the  crevices  of  talus   slopes;    others  burrow  in  fine 


THE  DISTRIBUTION  OF  ORGANIC  FORMS         337 

rock  waste  or  soil.  Name  some  animals  of  these  kinds. 
Some  animals  choose  steep  cliffs  and  high  peaks  for  their 
home,  so  that  they  shall  not  be  easily  pursued.  Eagles 
build  theii*  nests  on  inaccessible  pinnacles,  such  as  those 
of  the  spurs  that  separate  the  huge  side  ravines  of  the 
canyon  of  the  Colorado  in  Arizona.  What  can  you  tell 
about  the  home  of  the  Rocky  mountain  sheep  (the  bighorn) 
and  of  the  chamois  of  the  Alps  ? 

194.  Variation  of  Plants  and  Animals.  —  All  the  many 
existing  kinds  of  plant  and  animal  life  are  the  descendants 
of  a  smaller  number  of  more  ancient  kinds.  But  when 
the  ancient  forms,  preserved  as  fossils,  are  compared  with 
living  forms,  it  is  found  that  they  are  not  alike.  Through 
the  millions  and  millions  of  years  during  which  the  earth 
has  been  inhabited  there  have  been  slow  variations  in  the 
kinds  of  plants  and  animals  living  on  it,  so  that  those  now 
living  differ  from  their  remote  ancestors.  The  forms  of 
life  to-day  are,  as  a  rule,  very -unlike  those  whose  fossils 
are  found  in  the  oldest  fossil-bearing  rocks. 

Among  the  many  causes  which  have  combined  to  pro- 
duce variations  in  plants  and  animals,  none  have  been 
more  important  than  changes  in  their  geographical  sur- 
roundings. While  part  of  a  sea  bottom  is  slowly  raised 
to  form  a  coastal  plain,  the  kinds  of  animals  that  once 
occupied  this  part  of  the  sea  floor  must  seek  some  other 
home ;  at  the  same  time  the  plants  and  animals  of  the 
neighboring  older  land  have  opportunity  of  taking  pos- 
session of  the  young  plain.  As  lofty  mountains  are 
slowly  worn  down  to  lowland  peneplains,  the  forms  of 


338  ELEMENTARY  PHYSICAL  GEOGRAPHY 

life  that  once  occupied  the  higher  mountains  must  adapt 
themselves  to  their  new  surroundings  or  perish.  During 
the  slow  change  of  climate  which  caused  the  gradual 
advance  and  retreat  of  the  great  ice  sheets  that  once 
covered  eastern  Canada  and  the  northeastern  United 
States,  plants  and  animals  were  first  driven  away  from 
these  regions  and  later  allowed  to  return  to  them. 

Changes  of  these  kinds  have  repeatedly  taken  place 
in  the  earth's  history,  and  it  is  probable  that  every  one 
of  them  has  caused  some  variation  in  the  plants  and 
animals  of  their  regions.  The  plants  and  animals  that 
we  now  find  distributed  over  the  world  represent  the 
present  stage  in  the  long  series  of  varying  forms. 

195.  Life  in  the  Seas  and  on  the  Lands.  —  Xhe  different 
parts  of  the  earth  are  so  unlike  that  it  is  natural  to  find 
striking  differences  among  the  plants  and  animals  which 
have  become  fitted  to  occupy  unlike  regions.  No  geo- 
graphical contrast  is  greater  than  that  between  the  sea 
floors  covered  by  the  oceans  and  the  lands  covered  by  the 
air.  The  kinds  of  plants  and  animals  that  have  made  their 
home  on  the  lands  have  come  to  differ  greatly  from  those 
that  have  for  ages  lived  in  the  oceans.  Hence  continents 
and  oceans  must  have  existed  for  long  ages  because  their 
plants  and  animals  are  now  very  unlike. 

A  remarkable  difference  between  land  and  sea  life 
results  from  the  much  greater  density  of  water  than  of 
air.  Even  the  largest  sea  plants  do  not  need  strong 
trunks,  but  are  supported  by  the  water.  Many  sea  ani- 
mals are  no  heavier  than  the  water  they  live  in;  hence 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        339 

they  can  float  without  exertion  and  all  their  strength  can 
be  given  to  swimming.  The  kinds  of  fish  that  sometimes 
rest  on  the  water  bottom  lie  upon  it  so  lightly  that  they 
have  no  need  of  legs ;  all  their  members  are  fins.  Many 
kinds  of  fish  and  other  marine  forms  spend  their  lives  in  the 
open  ocean  without  approaching  the  shores  or  the  bottom. 

Birds,  on  the  other  hand,  are  much  heavier  than  the  air 
through  which  they  fly ;  hence  much  of  their  strength  must 
be  used  to  prevent  falling.  Even  the  best  flyers  spend 
some  of  their  time  on  the  ground  or  on  trees.  When  they 
alight  the  air  gives  them  so  little  support  that  they  need 
legs  on  which  to  walk  about. 

It  has  been  explained  in  earlier  chapters  that  the  deep 
ocean  is  monotonously  cold,  dark,  and  quiet,  without 
changes  of  weather  or  seasons,  and  that  the  ocean  bottom 
is  usually  a  gently  undulating  plain  covered  with  ooze  or 
mud  for  thousands  of  miles  together.  The  lands,  on  the 
other  hand,  are  the  seat  of  varied  conditions.  They  pos- 
sess a  great  variety  of  form  and  material ;  they  experience 
changes  from  day  to  night,  from  summer  to  winter;  they 
suffer  many  changes  of  weather  from  warm  to  cold,  from 
calm  to  stormy,  from  clear  to  cloudy,  from  dry  to  wet.  The 
development  of  the  higher  forms  of  life,  such  as  are  com- 
monly found  on  the  lands,  should  be  regarded  as  a  conse- 
quence of  the  great  variety  of  geographical  conditions 
found  there,  in  contrast  to  the  monotony  of  the  deep  ocean, 
where  the  forms  of  life  are  of  a  much  simpler  order. 

Nearly  all  the  flowering  plants  live  on  the  lands.  Water 
plants,  especially  those  of  the  sea,  are  of  a  simpler  kind. 
No  plants  live  on  the  dark  ocean  floor,  for  plants  cannot 


340  ELEMENTARY  PHYSICAL  GEOGRAPHY 

grow  without  sunlight.  Many  animals  of  the  sea  are 
attached,  plantlike,  to  the  bottom.  Others  move  slowly, 
like  starfish  and  shellfish;  still  others  float  with  the  drifting 
waters,  having  little  movement  of  their  own,  like  jellyfish. 
Only  the  more  highly  organized,  like  many  of  the  fishes, 
move  rapidly;  but  nearly  all  land  animals  move  about 
actively,  walking,  running,  or  flying. 

The  larger  and  more  important  land  animals  (mammals 
and  birds)  are  warm-blooded.  Most  sea  animals  are  cold- 
blooded, like  the  lower  animals  of  the  land.  The  only 
warm-blooded  animals  of  the  sea  (whales,  porpoises,  seals, 
etc.)  are  believed  to  be  the  descendants  of  ancient  land 
ancestors,  gradually  modified  for  the  marine  life  which  they 
have  adopted.  The  reason  for  this  belief  is  that  the  sea 
mammals  still  resemble  in  many  ways  the  mammals  of  the 
lands.  They  bear  their  young  alive  and  nourish  them  with 
milk  from  the  breast ;  they  must  come  to  the  surface  of 
the  sea  to  breathe,  for  unlike  fish  they  have  no  gills  by 
which  they  can  make  use  of  the  air  that  is  dissolved  in  sea 
water.  They  differ  from  land  mammals  only  in  ways  that 
make  them  better  suited  for  life  in  the  sea ;  their  legs  have 
been  modified  into  flippers  for  swimming  ;  and  those  forms 
which,  like  the  whales,  live  altogether  in  the  sea  no  longer 
have  fur,  like  the  land  animals  of  a  cold  climate,  but  are 
protected  from  the  cold  of  sea  water  by  a  layer  of  fat  or 
"blubber"  under  their  skin. 

Many  land  animals  have  developed  organs  for  the  pro- 
duction of  sound,  the  most  remarkable  sounds  being  the 
song  of  birds  and  the  speech  of  man.  The  animals  of  the 
sea  are,  with  hardly  an  exception,  silent. 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        341 

The  greater  intelligence  of  many  land  animals  than  of  sea 
animals  should  also  be  regarded  as  a  result  of  the  develop- 
ment of  land  animals  amid  a  greater  variety  of  geographical 
conditions  than  is  found  in  the  seas.  The  class  of  insects, 
almost  limited  to  the  lands,  furnishes  many  examples  of 
extraordinary  instincts,  such  as  those  of  bees  and  ants. 
Nest  building  by  birds,  house  building  by  beavers,  "  hom- 
ing" of  pigeons,  and 
trailing  (by  scent)  of  dogs 
are  examples  of  highly 
developed  instincts 
among  land  animals  that 
have  no  parallel  among 
the  animals  of  the  sea. 

The  wonderful  intel-  „     ,„'      T 

Fig.  180.    Beavers 

ligence  of  man  has  been 

developed  on  the  lands,  because  only  on  the  lands  is  to  be 
found  the  great  variety  of  form,  climate,  and  products 
which  can  stimulate  the  development  of  high  intelligence. 
It  would  have  been  as  impossible  for  man  to  develop  as  an 
inhabitant  of  the  dark  and  monotonous  ocean  floor  as  it 
has  been  for  civilization  to  arise  on  the  frozen  and  lone- 
some lands  of  the  Antarctic  regions. 

196.  Life  on  the  Continents.  —  The  arrangement  of  the 
continents  has  exerted  a  great  influence  on  the  distribution 
of  land  plants  and  animals.  It  has  been  stated  that  the  north- 
ern continents  are  nearly  united  around  the  Arctic  circle, 
and  that  three  great  extensions  of  this  northern  land  belt 
stretch  southward;  Africa  being  most  closely  associated 


342 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


with  the  northern  lands  of  the  Old  World,  South  America 
being  less  closely  associated  with  North  America,  while 
Australia  is  cut  off  from  Asia  by  the  sea.  It  is  there- 
fore natural  to  find  many  resemblances  among  plants 
and  animals  in  high  northern  latitudes,  and  to  find  that 
differences   among  them  become  greater  and  greater  as 

middle  and  low  latitudes  are 
passed  and  far  .  southern  lati- 
tudes are  entered. 

The  lichens  and  mosses  of  the 
frozen  northern  lands  are  similar 
all  around  the  Arctic  circle. 
The  animals  of  the  same  region 
include  the  polar  bear,  rein- 
deer (called  caribou  in  North 
America),  Ijoix,  musk  ox,  and 
Arctic  hare,  which  are  of  the 
same  kind  on  all  the  lands 
around  the  north  frigid  zone.  *  The  northern  lands  must 
therefore  have  once  been  connected,  and  their  connection 
must  have  occurred  at  so  late  a  period  in  the  history  of  the 
earth  that  there  has  not  since  then  been  time  enough  for 
these  Arctic  animals  to  become  unlike  in  their  now  some- 
what disconnected  homes. 

In  the  lower  latitudes  of  the  northern  hemisphere  the 
plants  and  animals  of  the  lands  possess  certain  resemblances 
that  prove  their  descent  from  a  common  ancestry,  but  they 
also  show  certain  marked  differences  that  prove  the  separa- 
tion of  the  continents  in  these  latitudes  for  a  very  long 
period  of  time. 


Fig.  181.    Caribou 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        343 

The  puma  and  jaguar  of  the  New  World  are  catlike 
animals  that  resemble  in  many  ways  the  lion  and  leopard 
of  the  Old  World.  The  resemblance  is  so  strong  that  it 
must  be  believed  they  are  descended  from  a  common  stock ; 
hence  in  some  former  time  the  Old  and  New  Worlds  must 
have  been  connected  in  latitudes  where  the  ancestors  of 
these  animals  could  pass  from 
one  region  to  the  other ;  but  this 
connection  ceased  so  long  ago 
that  distinct  differences  have 
since  then  arisen  between  the 
two  groups  of  catlike  animals. 

The  long  separation  of  the 
Old  and  New  Worlds  is  con- 
firmed by  finding  certain  plants 

and  animals  peculiar  to  each  region.  Horses,  cattle,  and 
other  domestic  animals,  as  well  as  tea,  coffee,  and  wheat, 
originated  in  the  Old  World,  while  humming  birds  and 
rattlesnakes,  as  well  as  maize  (corn),  potatoes,  and  cactus 
plants,  are  peculiar  to  the  New  World. 

The  differences  among  the  animals  of  the  three  southern 
continents  are  strongly  marked.  The  giraffe,  hippopotamus, 
and  many  kinds  of  antelopes  are  found  only  in  Africa ;  but 
that  continent  shares  with  the  adjacent  lands  of  southern 
Asia  the  lion,  elephant,  rhinoceros,  and  the  manlike  apes. 

South  America  stands  more  alone ;  here  are  found  mon- 
keys with  prehensile  tails,  tapirs,  llamas,  sloths,  and  arma- 
dillos, none  of  which  are  found  in  the  Old  World. 

In  Australia,  the  most  isolated  of  the  southern  conti- 
nents, nearly  all  the  quadrupeds  belong  to  the  peculiar 


344  ELEMENTARY  PHYSICAL  GEOGRAPHY 

group  of  marsupials  or  pouched  mammals,  which  carry  the 
young  in  a  pouch  on  the  breast  of  the  mother.  The  best 
known  marsupial  is  the  kangaroo.  Australia  contains  also 
the  lowest  kind  of  quadruped,  the  water  mole  (or  duckbill), 
which  resembles  birds  in  laying  eggs  from  which  its  young 
are  hatched. 

It  is  not  because  Australia  is  unfitted  for  mammals  that 

they  are  not  native  there. 
Rabbits  have  been  carried 
from  Europe  to  southern 
Australia,  where  they 
have  become  so  numerous 
as  to  be  a  nuisance.  Sheep 
are  now  raised  there  in 
great  numbers,  so  that 
Australia  has  become  an 
important  wool-growing 
FIG.  183.   Kangaroo  country.    The  absence  of 

mammals  in  Australia  must  therefore  be  explained  by  the 
long  separation  of  that  land  from  the  continents  on  which 
mammals  were  developed.  In  the  same  way,  the  absence 
of  Australian  forms  in  other  parts  of  the  world  is  not  due 
to  differences  of  food  supply  or  of  climate,  but  to  the  long 
separation  of  the  island-continent  from  the  other  lands. 
The  eucalyptus,  a  large  Australian  tree,  thrives  in  the  mild 
climate  of  California  and  southern  Europe.  So  horses  and 
cattle,  brought  from  Europe  to  the  New  World,  have 
become  numerous  on  the  prairies  and  plains  of  North 
America,  and  on  the  llanos  and  pampas  of  South  America. 
Potatoes,  native  to  America,  have  become  an  important 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        345 

food  supply  in  Europe.     What  can  you  tell  about  the 
English  sparrow? 

197.  Races  of  Mankind.  —  It  is  not  only  in  the  distri- 
bution of  the  lower  animals  that  the  grouping  of  the  con- 
tinents has  had  a  controlling  influence.  The  several  racfes 
of  mankind,  differing  in  language,  religion,  and  form  of 
government  as  well  as  in  color,  originally  occupied  regions 
that  correspond  in  a  general  way  to  the  grand  divisions  of 
the  lands.  Hence  it  may  be  believed  that  the  separation 
of  the  continents  by  the  oceans,  aided  by  certain  mountain 
and  desert  barriers,  has  been  the  chief  cause  of  the  division 
of  mankind  into  races. 

The  greatest  of  the  continents,  Eurasia,  contains  two 
races.  *  The  European  race,  generally  light  colored  but 
with  some  dark-skinned  families,  has  its  home  in  Europe, 
Africa  north  pf  the  Sahara,  and  southwestern  Asia.  The 
leading  nations  of  this  race  are  the  most  advanced  peoples 
of  the  world.  They  have  developed  liberal  governments 
in  which  the  rights  of  the  people  are  considered,  and  have 
advanced  greatly  in  the  cultivation  of  the  arts  and  sciences. 

The  Asian  race  is  found  chiefly  in  eastern,  central,  and 
northern  Asia ;  it  is  often  called  the  Yellow  race.  China 
contains  the  greatest  number  of  this  race,  the  Chinese 
being  separated  from  the  Hindus  of  India  (a  branch  of 
the  European  race)  by  the  lofty  mountains  of  the  Hima- 
layan system.  Although  comparatively  advanced  in  many 
arts,  the  Asians  have  acquired  little  knowledge  of  the 
sciences,  and  their  governments  are  usually  despotic.  The 
Japanese  are  to-day  their  most  advanced  nation. 


346  ELEMENTARY  PHYSICAL  GEOGRAPHY 

America  is  the  home  of  the  American  or  Red  race ;  its 
native  inhabitants  are  divided  into  many  tribes,  each  led 
by  a  chief.  Africa,  south  of  the  Sahara,  is  the  home  of  the 
African  or  Black  race,  governed  by  despotic  kings  or 
chiefs.  Australasia  and  the  peninsulas  and  islands  of 
southeastern  Asia  include  certain  black  and  brown  races. 
Few  nations  among  these  laces  have  made  important 
advances  toward  civilization. 

Within  the  last  few  centuries  the  means  of  travel  over 
land  and  sea  have  greatly  increased,  and  to-day  the  races 
of  mankind  are  by  no  means  limited  to  the  continents 
named  above  as  their  homes.  People  of  European  ancestry 
now  make  the  chief  part  of  the  population  in  North  and 
South  America,  southern  Africa,  Australia,  and  New 
Zealand,  as  well  as  in  Europe.  The  Chinese  are  not 
limited  to  China  alone,  but  are  found  as  merchants  and 
laborers  in  the  islands  of  southeastern  Asia,  Australia, 
and  elsewhere.  Many  descendants  of  the  African  race 
are  now  living  in  North  and  South  America. 

It  should  be  noticed  that,  while  the  people  of  the  Euro- 
pean race  are  now  widely  distributed  over  all  parts  of  the 
world)  and  while  Asians  and  Africans  are  found  in  large 
numbers  in  other  lands  than  their  homes,  few  of  the  less 
advanced  races  have  entered  Europe,  the  chief  of  these 
being  members  of  the  Asian  race,  the  Turks  in  the  south- 
east and  the  Finns  and  Lapps  in  the  north. 

198.  Life  on  Islands.  —  Islands  that  rise  from  conti- 
nental shelves  are  occupied  by  many  plants  and  animals 
similar  to  those  of  the  neighboring  mainland.    It  is  inferred 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        347 


from  this  that  the  continental  mass  once  stood  higher  than 
now  and  that  the  continental  shelf  was  then  a  lowland  on 
which  the  present  islands  rose  as  hills  or  mountains.  The 
forms  of  life  that  were  then  widespread  have  become  sepa- 
rated by  the  submergence  of  the  lowlands  and  the  division 
of  the  islands  from  the  continent. 

Various  species  of  cassowaries,  large  ostrichlike  birds 
unable  to  fly  or  swim,  are  found  in 
Australia  and  on  the  hilly  islands 
to  the  north,  each  land  area  having 
its  own  species.  From  this  it  is 
supposed  that  the  ancestral  family 
of  all  these  species  occupied  the 
region  when  the  continental  mass 
stood  higher  and  the  mainland  and 
islands  were  connected  by  the  low- 
land now  under  water  in  the  con- 
tinental shelf.  Since  then  it  is 
believed  that  the  region  has  been 
depressed  and  the  lowland  flooded 
by  the  sea,  while  the  higher  parts 
remain  as  islands  separated  from  Australia  and  from  each 
other.  The  differences  between  the  various  species  of 
cassowaries  must  have  arisen  since  their  family  was  divided 
by  the  drowning  of  the  lowlands. 

Many  of  the  islands  near  Australia  resemble  that  con- 
tinent in  possessing  marsupials.  The  islands  nearer  Asia 
have  no  marsupials,  but  possess  many  mammals  similar  to 
those  of  the  mainland  to  which  they  are  related.  A  belt 
of  deep  water  divides  the  two  groups  of  islands. 


Fig.  184.    Cassowary 


348  ELEMENTARY  PHYSICAL  GEOGRAPHY 

Islands  that  rise  from  the  deep  ocean  floor  far  from  the 
continents  have  no  large  native  animals,  but  are  occupied 
by  such  forms  of  animals  and  plants  as  might  have  reached 
themN  through  the  air  or  the  water  from  the  nearest  larger 
land. 

The  Azores,  a  group  of  mid-ocean  volcanic  islands  in 
the  North  Atlantic,  are  so  called  from  the  hawks  that 
were  common  there  when  the  islands  were  discovered  by 
voyagers  from  Europe.  The  Galapagos  islands  of  similar 
origin  in  the  Pacific  west  of  Peru  are  named  from  the 
large  tortoises  that  abound  on  them. 

199.  Climate  as  a  Control  of  the  Distribution  of  Plants 
and  Animals.  —  Differences  of  temperature  resulting  from 
the  globular  form  of  the  earth  are  of  great  importance  in 
limiting  the  distribution  of  plants  and  animals.  Plants 
like  palm  trees,  that  flourish  in  the  torrid  zone,  spread  into 
lands  of  higher  latitudes  on  both  sides  of  the  equator  until 
they  reach  regions  where  the  summers  are  too  cool  for 
them  to  mature  their  fruit.  Plants  that  occupy  the  tem- 
perate zones  are  limited  to  belts  on  whose  polar  side  the 
summer  is  too  brief  and  cool  and  on  whose  equatorial  side 
the  summer  is  too  hot  for  their  seeds  to  ripen.  Thus  in 
the  central  United  States  cotton  is  limited  to  the  southern 
states,  corn  flourishes  best  near  the  middle  of  the  country 
from  the  Ohio  to  the  lower  Missouri,  and  wheat  is  pro- 
duced most  abundantly  in  the  northern  states.  In  these 
northern  latitudes  there  are  great  forests  of  pines  and 
other  cone-bearing  trees.  Still  farther  north,  where  the 
ground  is  frozen  all  the  year  round,  except  for  a  little 


Plate  XVlll.     Forest  in  the  Eqiiatoiial  Kaiii  Belt,  Ceylon 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        349 

melting  during  the  sliort  summer,  trees  are  wanting  and 
vegetation  is  reduced  to  stunted  and  herbaceous  forms, 
with  many  mosses  and  lichens.     (See  Figure  112.) 

The  various  kinds  of  animals  are,  like  plants,  limited  to 
regions  in  which  the  summers  are  long  and  warm  enough 
—  but  not  too  warm  —  for  them  to  rear  their  young.  But 
unlike  plants,  which  live  on  mineral  food  derived  from  the 
soil  and  the  air,  animals  subsist  either  on  animal  or  vege- 
table food;  and  flesh-eating  animals,  like  the  lion,  often 
devour  .plant-eating  animals,  like  the  antelope.  Thus  in 
the  end  all  animals  depend  for  food  directly  or  indirectly 
on  plants;  hence  the  distribution  of  animals  depends  in 
part  on  the  distribution  of  plants,  and  this  in  turn  depends 
on  climate. 

Examples  of  the  distribution  of  animals  according  to 
zones  of  temperature  are  found  in  the  limitation  of  the 
caribou,  moose,  and  elk  to  the  northern  parts  of  America; 
of  the  alligator,  tapir,  and  sloth  to  low  latitudes;  and  of 
the  rhea  to  far  southern  America. 

200.  Climate  as  a  Control  over  the  Customs  of  Savage 
Tribes.  —  The  customs  of  mankind  are  influenced  in  many 
ways  by  climate.  Some  of  the  climatic  influences  are 
direct,  as  with  regard  to  clothing  and  shelter.  Some  influ- 
ences are  indirect,  as  with  regard  to  food  supply,  which  in 
turn  is  affected  by  the  distribution  of  plants  and  animals. 
Climatic  influences  are  less  apparent  on  civilized  people 
than  on  savage  tribes;  for  the  former  have  developed 
world-wide  commerce,  and  thus  gather  supplies  from  all 
parts  of  the  earth;  while  the  latter  know  little  or  nothing 


350  ELEMENTARY  PHYSICAL  GEOGRAPIfY 

of  regions  away  from  their  own  home.  Two  examples  are 
given  in  the  following  paragraphs. 

The  equatorial  belt  of  Africa  is  in  large  part  a  densely- 
forested  wilderness,  because  of  its  plentiful  rainfall.  Tall 
trees  spread  their  branches  aloft,  shading  the  ground  all  the 
year  with  their  heavy  foliage.  Vines  and  creepers  climb  the 
trees  and  hang  from  bough  to  bough  in  great  festoons,  and 
the  shady  and  damp  ground  is  covered  with  a  thick  growth 
of  bushes  with  stems  and  branches  so  closely  interlaced  that 
it  is  almost  impossible  to  make  one's  way  through  them 
without  cutting  a  passage.  Even  the  wild  animals  of  the 
forest  go  and  come  by  paths  that  they  keep  open  by  fre- 
quent passing.  Objects  near  at  hand  are  hidden  from  sight; 
the  explorer  cannot  tell  what  is  ahead  of  him  in  the  gloom 
of  the  forest  until  he  is  close  upon  it.  Vegetation  is  here 
so  luxuriant  that  it  is  a  burden  upon  the  people  who  live 
amid  its  abundant  growth. 

Some  of  the  savages  of  this  great  forest  are  Dwarfs,  from 
three  to  four  and  a  half  feet  in  height.  They  wear  little 
clothing,  for  the  air  about  them  is  always  warm.  They  do 
not  try  to  make  clearings  and  to  cultivate  fields,  but  search 
out  the  more  open  parts  of  the  forest  and  build  their 
villages  where  the  undergrowth  is  least  dense.  They  have 
some  trade  with  other  tribes,  but  live  chiefly  by  hunting 
wild  game,  which  is  plentiful.  Although  entirely  ignorant 
of  many  simple  arts  practiced  by  people  of  more  open 
countries,  the  Dwarfs  are  expert  in  all  the  ways  of  forest 
life.  They  can  travel  quickly  through  the  woods,  know- 
ing all  the  paths  and  open  places.  They  protect  their 
villages  from  the  attack  of  neighboring  tribes  by  planting 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        361 

sharpened  stakes  in  the  paths  of  approach.  They  dig  pit- 
falls in  the  narrow  forest  paths,  covering  them  with  sticks 
and  leaves,  and  in  this  way  capture  even  the  larger  wild 
animals.     They  prepare  a  poison  from  certain  plants  and 


Fig.  185.    Dwarfs  in  the  Equatorial  Forest 

tip  their  spears  and  arrows  with  it.  In  spite  of  their  small 
size  they  are  formidable  enemies  to  invaders  of  their  forest 
home. 

The  desolate  shores  of  Greenland  present  conditions  of 
an  entirely  different  kind.  Extreme  cold  prevails  there 
during  the  long  dark  winter,  and  most  of  the  land  is 
covered  all  the  year  round  with  ice  and  snow, — a  vast  cold 


352 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


desert.  A  narrow  belt  along  the  coast  is  free  from  snow- 
in  summer,  and  here  live  a  few  tribes  of  Eskimos;  but 
the  ground  is  so  barren  that  they  get  little  support  from 
it.  The  only  treelike  plants  are  of  stunted  growth,  sel- 
dom over  two  or  three  feet  high.  The  herbage  consists 
chiefly  of  mosses  and  lichens,  which  grow  for  a  time  in 
summer  when  the  frozen  ground  is  thawed  for  a  few  inches 

below  the  surface.  A 
small  supply  of  wood 
comes  from  the  trunks  of 
trees  that  are  occasion- 
ally drifted  by  ocean  cur- 
rents-to  the  Arctic  shores 
from  warmer  regions ; 
but  there  is  so  little  of  it 
that  many  articles  which 
might  be  made  of  wood  elsewhere  are  here  made  from  the 
bones  of  sea  animals. 

The  Eskimos  wear  heavy  fur  clothing.  They  travel  in 
sleds  drawn  by  dogs  over  the  snow-covered  land  or  the 
frozen  sea.  They  make  slender  canoes,  called  kayaks, 
which  they  paddle  very  skillfully  when  hunting  seals  and 
walruses.  Until  visited  by  Europeans  and  Americans,  the 
Eskimos  were  as  ignorant  of  the  rest  of  the  world  as  were 
the  African  Dwarfs;  yet  so  well  have  they  learned  to  take 
every  advantage  of  their  frigid  surroundings  that  they  sur- 
vive where  men  from  a  more  civilized  nation,  unused  to 
living  in  so  barren  a  region,  might  perish. 

These  brief  accounts  of  the  Dwarfs  and  the  Eskimos  show 
very  clearly  that,  as  a  rule,  the  climate  and  the  other  local 


Fig.  186.    Eskimo  hunting  Walrus 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        353 

features  of  the  regions  in  which  they  live  exercise  a  strong 
control  oyer  their  manner  of  living.  The  Eskimos  know 
nothing  of  forests,  thickets,  and  pitfalls.  The  Dwarfs 
know  nothing  of  snow  and  ice,  sleds,  kayaks,  and  har- 
poons. But  each  of  these  groups  of  people  has  become  well 
practiced  in  certain  habits  and  customs  that  enable  them 
to  secure  food,  shelter,  and  reasonable  safety  of  life;  and 
these  habits  and  customs  are  closely  related  to  the  surround- 
ings in  which  they  have  been  acquired.  The  further  the 
world  is  examined,  the  more  general  this  rule  is  found  to  be. 

201.  Effects  of  Change  of  Seasons  on  Plants  and  Animals. 
—  In  the  torrid  zone  the  chief  seasonal  contrasts  of  the 
year  are  between  the  dry  (hot)  and  wet  seasons.  During 
the  dry  season  vegetation  withers,  but  with  the  coming 
of  the  wet  season  all  forms  of  plant  life  grow  actively. 
This  is  particularly  marked  on  the  desert  borders  of  the 
subequatorial  rain  belt,  where  the  ground  may  be  bare  and 
dusty  in  the  dry  season  and  covered  with  vegetation  in 
the  wet  season,  as  on  the  llanos  of  Venezuela. 

In  higher  latitudes  the  chief  seasonal  contrasts  are 
between  the  cold  and  warm  seasons,  or  winter  and  sum- 
mer. In  winter  vegetable  growth  is  almost  or  quite  sus- 
pended, but  with  the  approach  of  summer  growth  begins. 
Some  trees,  like  the  pines,  bear  the  winter  with  little  vis- 
ible change.  Others,  like  the  oaks,  drop  their  leaves  in  the 
autumn,  and  hence  this  season  is  often  called  fall.  Trees 
of  this  kind  pass  the  winter  with  bare  branches.  Still  other 
plants  are  killed  by  the  coming  of  cold  weather,  and  only 
their  seeds  survive  the  winter  \  these  are  called  annuals. 


354  ELEMENTARY  PHYSICAL  GEOGRAPHY 

Animals  also  have  many  devices  for  surviving  the 
winter.  Some  are  hardy  enough  to  bear  all  sorts  of 
weather,  and  may  be  seen  searching  for  food  through 
winter  cold  as  well  as  summer  heat ;  wolves  and  foxes  are 
of  this  kind.  Others  retreat  into  caverns  and  crevices 
and  lie  torpid  during  the  cold  months,  coming  forth  lean 
and  hungry  in  the  spring;  bears  and  snakes  have  this 
habit.  Many  insects  are  like  the  annual  plants  in  being 
killed  by  cold  weather,  leaving  their  eggs  to  be  hatched 
on  the  return  of  higher  temperatures  in  the  spring.  Many 
birds  escape  winter  weather  by  migrating  to  a  warmer  region 
in  the  autumn  and  returning  poleward  in  the  spring. 

All  these  peculiar  habits  result  from  the  oblique  position 
of  the  earth's  axis  with  respect  to  the  plane  of  its  orbit,  by 
which  the  change  of  seasons  is  caused. 

Changes  in  habit  of  life  with  changes  of  season  are 
not  limited  to  plants  and  the  lower  animals.  Man  also 
responds  in  many  ways  to  seasonal  changes  from  heat'  to 
cold,  from  dryness  to  rainfall.  In  continental  interiors 
of  temperate  latitudes,  where  most  of  the  rainfall  is  in 
summer,  the  wandering  of  nomadic  tribes  is  largely  con- 
trolled by  search  for  pasture  for  their  flocks;  as  on  the 
plains  or  steppes  north  of  the  Caspian  sea.  Again,  in 
Algeria,  on  the  northern  border  of  the  Sahara,  summer 
pasture  is  found  chiefly  on  the  mountain  slopes ;  but  when 
the  winter  rains  begin  (subtropical  rains)  the  herdsmen 
drive  their  flocks  down  to  the  lower  lands,  that  were  dusty 
and  barren  deserts  a  few  months  before. 

Planting  and  harvesting  are  characteristic  occupations 
of  the  warmer  months  among  the  more  advanced  peoples 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        355 

in  all  temperate  climates ;  during  the  colder  months  agri- 
cultural labor  is  in  less  demand.  In  the  north  temperate 
zone  there  is  the  great  advantage  of  an  abundant  land  area 
with  a  winter  that  is  cold  enough  to  require  the  storage  of 
food  and  a  summer  that  is  warm  enough  to  provide  the 
food  to  be  stored.  The  leading  nations  of  the  world  have 
arisen  in  this  zone,  and  there  can  be  little  doubt  that  the 
habits  of  industry  and  thrift  here  made  necessary,  but 
not  too  difficult,  by  geographical  conditions  have  been  of 
great  importance  in  bringing  civilization  out  of  savagery. 

202.  Plant  and  Animal  Life  on  Lofty  Mountains.  — 
Climate  varies  not  only  from  equator  to  pole,  but  also  from 
lowlands  to  mountains.  On  account  of  the  lower  temperar 
ture  and  the  heavier  rainfall  and  snowfall  of  high  mountains, 
theu'  plants  and  animals  are  unlike  those  living  on  the  sur- 
rounding lowlands.  On  lofty  moimtain  flanks  in  the  tem- 
perate zone,  hardy  cone-bearing  trees  usually  succeed  trees 
that  need  a  milder  climate.  As  the  limit  of  tree  growth,  or 
the  "  tree  line,"  is  approached  only  stunted  and  deformed 
trees  survive.  Then  comes  a  belt  in  which  the  slopes  bear 
grass  and  Alpine  flowers.  (Alpine  is  used  to  refer  not  only 
to  the  European  Alps,  but  also  to  the  animals  and  plants  of 
any  lofty  mountain.)  Following  this  is  the  lower  limit  of 
summer  snow  banks,  or  the  "  snow  line,"  above  which  some 
of  the  snow  of  one  winter  lasts  over  the  following  summer, 
thus  excluding  plant  life.  It  is  remarkable  that  many  plants 
found  near  the  snow  line  on  mountains  in  the  warmer  zones 
are  also  found  near  sea  level  in  the  frigid  zone,  although 
they  are  wanting  on  the  low  ground  between  the  two. 


356 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Many  animals  survive  in  mountains  after  disappearing 
from  the  surrounding  lower  ground.     Various  kinds  of 


Fig.  187.     Stunted  Trees  at  the  Tree  Line  on  the  Slope  of  Pikes  Peak 


ibex  (mountain  goat)  are  found  on  the  mountains  of 
Eurasia,  each  range  having  its  own  peculiar  species.  All 
are  derived  from  a  common  ancestry 
on  the  intermediate  lower  lands;  but 
since  they  have  been  limited  to  moun- 
tain homes,  the  animals  in  each 
range  have  varied  in  their  own  way, 
independently  of  the  others,  and  have 
thus  come  to  be  unlike.  This  is  a 
remarkable  illustration  of  the  effect 
of  mountains  in  keeping  their  inhab-  ^^^'  ^^^'    ^^^^ 

itants  apart  from  the  rest  of  the  world;  it  may  be  com- 
pared with  the  effect  of  isolation  on  islands. 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        357 

A  species  of  butterfly  living  on  the  White  mountain 
summits,  in  New  Hampshire,  is  unlike  the  species  of  the 
surrounding  lower  ground,  but  resembles  those  of  more 
northern  lands.  The  top  of  Mt.  Katahdin,  an  isolated 
mountain  in  northern  Maine,  possesses  a  similar  butterfly, 
but  it  varies  somewhat  from  the  one  on  the  White  moun- 
tains, the  variation  having  taken  place  since  the  butterflies 
of  the  two  districts  were  isolated  on  their  mountain  homes, 

203.  The  Effect  of  Mountains  on  their  Human  Inhab- 
itants.—  It  has  already  been  stated  that  the  deep  valleys 
of  lofty  mountains  have  often  been,  used  as  retreats  by  the 
people  of  a  nation  that  has  been  driven  from  the  neigh- 
boring lower  land  by  the  invasion  of  a  stronger  nation. 
The  following  examples  may  be  cited. 

The  Basques  live  in  the  northern  valleys  of  the  Pyrenees, 
near  the  angle  of  the  Bay  of  Biscfuy.  They  are  probably 
descendants  of  the  Iberians,  an  ancient  people  who  occu- 
pied a  large  part  of  Spain  and  France,  from  which  they 
had  been  driven  by  invaders  even  before  Csesar  made 
those  countries  subject  to  Rome,  nearly  2000  years  ago. 
The  Basque  language  is  the  only  surviving  form  of  Iberian, 
and  is  entirely  unlike  other  European, languages. 

The  Svanetians  occupy  deep  inner  valleys  in  the  Cau- 
casus mountains,  with  difficulty  accessible  from  the  outer 
country.  They  are  the  descendants  of  an  ancient  people 
who  occupied  a  much  more  extensive  territory,  from  which 
they  were  driven  back  to  the  mountains  many  centuries 
ago.  There  ancient  customs  and  a  peculiar  language  are 
preserved;  there  the  people  still  live  entirely  apart  from 


358  ELEMENTARY  PHYSICAL  GEOGRAPHY 

the  ways  of  modern  times.  Although  daring  and  patri- 
otic, they  are  ignorant  and  superstitious.  Their  wretched 
houses  are  dark  and  dirty;  their  roads  are  only  rough 
tracks.  Arts  and  industries  are  of  the  simplest  order ; 
trade  is  only  by  barter. 

The  people  who  live  in  deep  valleys  among  lofty  moun- 
tains find  life  more  difiicult  than  do  those  who  live  on  open 
plains.  The  difference  between  the  two  cases  is  in  large 
part  due  to  the  action  of  gravity  on  the  mountain  sides. 
The  peculiar  dangers  of  avalanches  and  landslides  are 
directly  the  result  of  gravity.  The  finer  waste  on  the 
steep  slopes  is  rapidly  washed  down  by  active  rivulets. 
The  stony  soil  that  remains  cannot  be  easily  cultivated, 
and  if  it  is  spaded  or  plowed,  much  of  it  will  be  washed 
away  by  the  next  heavy  rain. 

The  valley  floors  are  narrow,  giving  little  room  for  fields. 
The  streams  flow  swiftly  down  their  sloping  channels; 
their  torrential  current  is  too  strong  to  be  navigated ;  their 
floods  are  frequent  and  destructive.  It  is  difficult  to  pass 
from  one  valley  over  the  dividing  ridge  to  the  next  valley 
because  of  the  labor  of  climbing  up  and  down  the  slopes. 
Hence,  although  mountaineers  are  active  and  hardy,  they 
are  not,  as  a  rule,  great  travelers  or  traders.  The  people  of 
one  valley  know  little  of  those  a  few  score  miles  away, 
a  distance  that  would  be  considered  a  trifle  by  a  horse- 
man on  a  plain.  The  people  of  neighboring  valleys  are 
often  distinguished  by  slight  differences  in  their  common 
language. 

During  winter  mountain  valleys  may  receive  a  heavy 
snowfall.     Then  for  a  season  the  people  and  their  flocks 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        359 

are  gathered  in  the  lower  villages,  living  on  supplies  stored 
up  from  the  previous  summer.  In  summer,  when  the  snows 
are  melted  from  the  mountain  sides,  cattle,  sheep,  and  goats 
are  driven  up  from  the  valleys  to  pasture  on  the  grassy- 
slopes  of  the  ridges.  Hay  is  carried,  often  on  the  backs 
of  the  mountaineers,  down  to  the  villages  for  winter  need. 

204.  Life  in  Deserts.  —  Climate  exerts  a  powerful  con- 
trol over  the  distribution  of  life  through  differences  of  rain- 
fall. This  control  is  well  illustrated  by  the  conditions  of 
those  regions  where  rainfall  is  deficient.  Plant  and  animal 
life  is  scanty  in  deserts  Because  of  the  difficulty  of  secur- 
ing food  and  water.  The  dryness  of  the  soil  is  unfavorable 
to  plant  growth.  Leaves  are  small  or  wanting,  for  thus 
the  loss  of  water  by  evaporation  from  the  leaf  surfaces  is 
diminished.  Thorns  are  commonly  developed,  like  so  many 
signs,  "keep  off,"  as  if  to  lessen  the  chance  of  injury  to 
the  plant  in  a  region  where  living  is  so  difficult  that  every 
aid  must  be  summoned  to  protect  life. 

During  long  droughts  an  arid  region  may  seem  almost 
free  from  vegetation.  If  rain  falls,  small  plants  spring  up 
everywhere,  refreshing  the  surface  with  their  green  color, 
but  soon  withering  away  in  the  succeeding  dry  period. 
On  the  desert  slopes  of  Peru,  where  droughts  may  last 
four  or  five  years,  plants  soon  spring  up  after  a  shower. 
These  examples  show  that  the  plants  of  arid  regions 
possess  great  vitality. 

The  larger  plants  of  arid  regions  are  thinly  scattered, 
leaving  much  bare  surface.  There  is  no  striving  for  space, 
such  as  commonly  occurs  in  well-watered  regions,  where 


360 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


plants  of  more  active  growth  may  crowd  out  the  weaker 
forms.  Dry  regions  seldom  produce  useful  plants.  Trees 
are  small,  and  their  wood  is  hard  and  knotted;  they  cast 
little  shade  on  the  dry,  bare  ground.     The  sagebrush,  so 

abundant  on  the  arid 
western  plains  of  the 
United  States,  finds 
little  use  except  as 
an  inferior  firewood. 
The  animals  of  des- 
erts are  generally  of 
dull  or  gray  color,  not 
easily  seen  on  the  bar- 
ren surface.  Many 
of  them  are  fleet  in 
movement,  like  the 
antelope,  or  of  great 
endurance  under  a 
small  supply  of  food 
and  water,  like  the 
camel.  Those  which  are  sluggish  are  often  venomous, 
like  the  tarantula,  the  scorpion,  and  the  rattlesnake. 


Fig.  189.    The  Yucca,  a  Desert  Tree 


205.  The  People  of  Deserts.  —  The  human  inhabitants  of 
arid  deserts  are  few  and  miserable  as  compared  with  the 
more  favored  races  of  the  world.  Their  food  supply  is 
scanty  and  of  little  variety.  Their  arts  are  primitive,  for 
raw  materials  are  of  few  kinds.  They  possess  strength  and 
endurance,  without  which  life  would  be  impossible  under 
the  difficulties  around  them ;  they  have  a  keen  intelligence 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        361 

for  every  advantage  that  their  desert  home  affords,  but 
they  cannot  rise  above  a  low  stage  of  development. 

Many  of  the  wandering  tribes  of  the  Sahara  find  the 
struggle  for  existence  so  severe  that  they  and  their 
animals  are  often  on  the  verge  of  starvation.  They  must 
move  from  place  to  place  to  secure  food ;  hence  they  do  not 
build  houses,  but  live  in  tents  that  can  be  easily  carried 
about  as  they  wander  from  one  pasture  ground  to  another. 
As  a  result  of  their  wandering  habits,  they  have  come  to 
be  excellent  horsemen  and  show  great  endurance  in  sur- 
viving the  hardships  that  they  must  often  suffer.  But,  on 
account  of  being  nearly  destitute,  they  have  the  habit  of 
taking  what  they  want  from  any  passing  travelers  whom 
they  can  plunder.  They  have  thus  preserved  into  modern 
times  a  rude  manner  of  life  which  must  have  been  universal 
in  the  early  history  of  mankind,  but  which  has  been  given 
up  in  recent  centuries  by  the  people  of  more  advanced 
nations,  among  whom  theft  is  now  punished  as  a  crime. 

The  Papago  Indians  of  the  Sonoran  region,  south  of 
the  Gila  river  (southwestern  United  States,  northwestern 
Mexico),  move  from  place  to  place  with  the  failing  and 
flowing  of  springs.  They  are  noted  for  strength,  speed, 
endurance,  and  abstinence.  The  Seri  Indians,  living  in 
the  desert  on  the  border  of  the  Gulf  of  California,  have  no 
horses  and  are  noted  as  runners. 

206.  Oases.  —  Fixed  settlements  in  desert  regions  are 
controlled  by  the  presence  of  water.  They  are  commonly 
made  where  springs  or  streams  flow  upon  the  open  country 
at  the  base  of  uplands  and  mountains ;  or  near  the  ends  of 


362  ELEMENTARY  PHYSICAL  GEOGRAPHY 

such  streams,  where  the  water  can  be  distributed  in  irri- 
gating canals;  or  at  points  where  ground  water  may  be 
found  in  the  nearly  dry  channels  of  withered  streams. 
Such  settlements  are  called  oases  in  the  Sahara,  and  the 
same  name  may  be  used  elsewhere. 


Fig.  190.    El  Kantara  Oasis,  Algerian  Sahara 

The  barrenness  of  many  deserts  is  due  simply  to  their 
dryness  and  not  to  an  unfavorable  composition  of  rock  or 
soil.  Where  springs  or  streams  moisten  the  soil,  grass 
and  trees  may  grow  naturally.  If  the  surface  can  be 
irrigated,  its  productiveness  may  be  increased  so  as  to 
support  permanent  settlements. 

The  contrast  between  a  habitable  spot  and  the  surround- 
ing barrenness  is  so  grateful  that  "  an  oasis  in  the  desert " 
has  come  to  serve  as  a  poetic  figure.  But  oases  are  only 
relatively  delightful.  Their  water  supply  is  often  limited 
and  impure;  their  products  are  few  in  variety  and  small 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        363 

in  quantity;  their  industries  are  primitive;  their  inhab- 
itants have  to  suffer  the  disadvantages  of  isolation  as 
completely  as  do  the  people  of  islands. 

The  oasis  of  Siwa,  in  the  Sahara,  350  miles  west  of 
Cairo,  "•  the  first  halting  place  on  the  great  desert  highroad 
to  the  west,''  is  still  little  changed  from  its  condition  in 
ancient  times.  Seclusion  seems  to  have  bred  mistrust,  for 
strangers  are  looked  on  as  intruders.  They  and  their 
modern  ways  of  doing  things  are  unwelcome. 

It  sometimes  happens  that  a  river  rising  in  well- watered 
regions  flows  across  a  desert  on  its  way  to  the  sea.  If  the 
river  has  developed  an  open  and  accessible  valley,  nearly 
all  the  population  of  the  region  is  gathered  on  its  flood 
plain. 

The  most  famous  river  of  this  kind  is  the  Nile,  which 
flows  1000  miles  through  the  desert  without  receiving  a 
branch,  except  a  few  small  wet-weather  streams.  Its  flood 
plain,  several  hundred  feet  below  the  desert  uplands 
that  inclose  it,  is  about  500  miles  long  and  from  5  to  15 
miles  wide,  broadening  on  the  delta  to  over  100  miles. 
Here  most  of  the  millions  of  Egyptians  dwell.  Their 
resources  are  almost  wholly  agricultural  and,  as  such, 
depend  on  the  annual  inundation  of  the  Nile,  caused  by 
the  northward  movement  of  the  belt  of  equatorial  rains 
over  the  upper  branches  of  the  river  in  summer.  The  flood 
begins  in  June,  usually  rising  twenty-five  feet  or  more  at 
Cairo  in  late  summer  or  early  autumn.  For  thousands  of 
years  the  fertility  of  the  flood  plain  has  been  maintained 
by  the  annual  additions  of  river  silt,  estimated  to  amount 
to  four  and  a  half  inches  a  century.     Still  better  use  of 


364  ELEMENTARY  PHYSICAL  GEOGRAPHY 

natural  conditions  is  about  to  be  made  by  building  a  strong 
dam  across  the  Nile  on  a  reef  of  rocks  that  forms  the  first 
cataract,  at  Assouan,  and  thus  storing  in  a  reservoir  a 
large  volume  of  water  for  irrigation  that  would  otherwise 
run  to  the  sea  unused. 

207.   Geographical  Factors  in  the  Life  of  Civilized  Peoples. 

—  It  has  already  been  shown  that  the  simplest  examples 
of  the  relations  of  man  and  nature  are  to  be  found  in  the 
life  of  savages,  who  know  few  arts  and  have  little  inter- 
course with  other  peoples  and  who  are  therefore  directly 
dependent  on  the  simplest  home  products.  What  can  you 
say  in  this  connection  about  the  natives  of  coral  islands  ? 

Civilized  nations  offer  much  more  complicated  exam- 
ples of  these  relations.  Here  the  people  are  engaged  in 
agriculture,  manufactures,  and  commerce.  Arts  and  trades 
are  highly  developed ;  the  products  of  many  parts  of  the 
world  are  gathered  and  skillfully  manufactured  into  a 
great  variety  of  articles  for  use  at  home  and  abroad.  It 
might  at  first  seem  as  if  such  a  people  had  overcome 
geographical  controls ;  but  closer  study  will  always  show 
that  they  are  influenced  by  them  on  all  sides,  and  that 
their  progress  is  less  dependent  on  overcoming  geograph- 
ical obstacles  than  on  taking  advantage  of  geographical  aids. 

In  savage  tribes  there  are  so  few  things  to  do  that  every 
man  is  well  practiced  in  nearly  all  the  duties  of  a  man's 
life.  In  civilized  nations  man's  work  has  become  greatly 
diversified,  and  "  a  jack  of  all  trades  is  master  of  none.'* 
Many  occupations  are  immediately  dependent  on  geograph- 
ical factors,  and  the  skill  needed  in  them  is  so  great  that 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        365 

few  persons  are  successful  in  more  than  one.  A  miner,  a 
farmer,  a  sailor,  each  knows  his  own  work  but  would  be 
at  a  loss  in  the  work  of  his  neighbors. 

Some  of  the  ways  in  which  men  gain  a  living  require  a 
very  close  acquaintance  with  geographical  details.  A  river 
pilot  must  know  all  the  bends  and  shoals  in  a  river  channel 
and  must  learn  how  they  are  changed  by  the  action  of  the 
river  in  scouring  away  or  building  up  the  banks  and  in 
sweeping  waste  along  the  bed. 

Certain  peculiar  occupations  are  dependent  on  a  variety 
of  geographical  conditions.  For  example,  in  stormy 
weather  the  schooners  that  sail  between  our  Atlantic 
ports  sometimes  anchor  in  shallow  water  near  the  shore. 
In  very  severe  storms  the  cables  may  break  and  the 
anchors  are  then  lost.  But  anchors  are  valuable;  hence 
men,  known  as  "anchor  draggers,"  make  a  business  of 
searching  for  them.  They  sail  in  pairs  and  drag  a  strong 
rope  between  their  vessels  -over  the  sea  bottom  in  fre- 
quented anchorage  grounds,  and  they  know  their  curious 
trade  so  well  that  they  make  a  living  by  selling  the 
anchors  that  they  find.  Can  you  give  some  other  examples 
of  this  kind? 

A  member  of  an  isolated  savage  tribe  depends  for  food, 
clothing,  weapons,  and  dwelling  upon  what  he  finds  close 
to  his  home ;  if  work  is  needed  in  building  a  hut,  in  secur- 
ing food,  in  making  clothing  or  weapons,  it  is  usually  done 
by  each  family  separately.  There  are  no  mills  where  flour 
is  ground  wholesale;  there  are  no  factories  where  cloth  is 
woven;  there  are  no  shops  where  household  supplies  can 
be  bought. 


366  ELEMENTARY  PHYSICAL  GEOGRAPHY 

In  a  civilized  country  a  family  may  occupy  a  house  which 
they  had  no  share  in  building  and  which  required  for  its 
construction  the  labor  ot  many  men  in  many  trades, — 
masons,  carpenters,  plumbers,  plasterers,  and  painters. 
The  materials  used  in  building  the  house  may  have  been 
brought  from  hundreds  of  miles  away.  The  stone  for  the 
foundation,  the  lime  for  mortar,  the  cement  for  the  cellar 
floor,  the  clay  for  bricks  in  the  chimney,  the  plaster  for  the 
walls  are  products  of  quarries  and  pits  in  different  dis- 
tricts. The  beams  for  the  frame,  the  boards  for  the  walls 
and  floors,  the  shingles  for  the  roof  have  probably  come 
from  different  forests. 

The  furniture  may  be  made  from  various  kinds  of  wood, 
metal,  and  cloth,  gathered  from  far  and  wide,  put  together 
in  great  factories,  and  distributed  for  sale.  The  carpets 
are  very  likely  spun  from  wool  from  the  pampas  of  South 
America.  The  iron  in  the  kitchen  utensils  probably  comes 
from  iron  ore  in  the  old  worn-down  mountain  region  west 
of  Lake  Superior,  smelted  with  coal  from  the  dissected 
plateau  of  western  Pennsylvania;  the  tin  of  tinware  prob- 
ably comes  from  the  Malay  peninsula  southeast  of  Asia. 
The  crockery  may  be  from  the  lowland  clay  belt  of  the 
New  Jersey  coastal  plain. 

The  daily  food  may  include  bread  from  flour  ground  by 
the  water  power  of  a  displaced  river  in  Minnesota  from 
wheat  grown  in  the  rich  drift  soils  of  the  northern  prairies 
or  in  the  deep-weathered  soils  of  the  lava  plains  of  Washing- 
ton, beef  from  the  cattle  ranches  of  the  Great  plains,  tea 
from  China,  coffee  from  Brazil,  sugar  from  Cuba,  and  salt 
from  New  York.     The  production  of  all  these  materials 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        367 

depends  on  such  geographical  factors  as  rock,  soil,  and 
climate.  Their  preparation  has  required  skilled  labor  of 
many  kinds,  in  which  natural  forces  are  usually  employed. 
Their  transportation  has  been  over  lands  and  seas,  along 
routes  influenced  by  geographical  conditions  at  every  turn. 
The  family  for  whose  comfort  all  these  threads  of  activity 
meet  in  a  single  house  may  be  that  of  a  typesetter,  skillful 
in  his  own  work,  but  unprepared  to  take  part  in  any  one 
of  the  many  arts  and  trades  on  which  his  home  comforts 
depend.  He  would  be  almost  helpless  alone;  but  if  he 
and  every  one  else  works  faithfully  and  well,  each  one  doing 
his  chosen  task  to  the  best  of  his  ability,  the  whole  nation 
thrives.  Yet  civilized  life  is  so  complicated  that,  until 
attention  is  directed  to  its  separate  items,  one  might  fail  to 
notice  how  largely  they  are  determined  by  geographical 
controls. 

How  many  kinds  of  materials  can  you  name  that  were  used  in 
the  house  you  live  in  ?  How  many  of  these  materials  can  you  trace 
back  to  their  sources  ?  From  how  many  different  states  or  countries 
did  they  come  ?  What  natural  forces  have  been  employed  in  pre- 
paring the  materials  for  use  ?  How  have  the  materials  been  brought 
to  their  place  of  use  ?  Similar  questions  may  be  asked  concerning 
furniture,  food,  and  clothing. 

208.   The  Influence  of  Geographical  Factors  on  History. — 

The  progress  of  history  has  been  repeatedly  influenced  by 
geographical  factors.  It  is  fortunate  for  the  modern  his- 
tory of  America  that  the  Atlantic  is  narrower  than  the 
Pacific;  it  is  chiefly  for  this  reason  that  the  New  World 
has  been  peopled  by  emigrants  from  the  leading  races  in  the 
western  part  of  Europe,  instead  of  from  the  less  advanced 


368  ELEMENTARY  PHYSICAL  GEOGRAPHY 

peoples  of  eastern  Asia.  The  eastern  coast  of  North  America 
has  abundant  harbors  where  the  newcomers  found  safe 
refuge  for  their  vessels.  All  the  early  settlements,  many 
of  which  have  now  become  important  seaboard  cities,  were 
located  on  these  protected  embayments  of  the  coast  line; 
none  of  them  were  established  on  exposed  headlands. 

The  boundaries  of  the  several  colonies  founded  by  the 
immigrants  were  in  most  cases  established  with  regard  to 
the  harbors  on  which  the  more  important  settlements  had 
been  made.  The  small  size  of  several  of  the  colonies,  and 
of  the  states  that  now  represent  them,  was  determined  by 
the  occurrence  of  bays  or  rivers  to  the  west,  where  other 
colonies  were  formed.  Rhode  Island,  founded  by  settle- 
ments on  the  drowned  valley  known  as  Narragansett  bay, 
was  limited  on  the  west  by  the  colony  which  took  posses- 
sion of  the  lower  Connecticut  valley;  and  Connecticut  was 
in  turn  limited  by  New  York,  whose  inland  growth  from 
its  excellent  harbor  was  guided  northward  by  the  drowned 
valley  of  the  Hudson.  New  Jersey  was  cut  off  from  west- 
ward growth  by  Pennsylvania,  whose  chief  city  was  estab- 
lished near  the  head  of  the  drowned  lower  part  of  a  valley, 
known  as  Delaware  bay.  The  small  state  of  Delaware  was 
limited  on  the  west  by  Maryland,  founded  on  Chesapeake 
bay,  the  drowned  lower  valley  of  the  Susquehanna;  and 
Maryland  was  in  turn  limited  by  Virginia,  to  whose  terri- 
tory the  Potomac  embayment  of  the  partly  drowned  coastal 
plain  gave  easy  access  west  of  Maryland.  Farther  south 
there  are  no  important  bays  or  rivers  along  the  Atlantic 
coast  with  a  north  and  south  trend,  and  there  are  no  more 
small  states. 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        369 

Mention  some  geographical  factors  on  which  the  importance  of 
New  York  city  depends;  of  Chicago;  of  San  Francisco.  Mention 
some  factors  on  which  the  small  population  of  the  Appalachian 
highlands  and  the  great  population  of  the  prairie  states  depend. 

Success  in  warfare  has  often  been  influenced  directly  or 
indirectly  by  geographical  factors.  The  size  of  an  army  is 
largely  the  consequence  of  such  factors  as  the  area,  form, 
climate,  and  fertility  of  the  country  to  which  it  belongs; 
the  strength  of  the  less  civilized  nations  has  therefore  often 
been  measured  by  the  number  of  their  warriors.  The 
character  of  soldiers  is  largely  dependent  on  the  habits  of 
the  community  from  which  they  are  enlisted.  Regiments 
of  infantry  recruited  from  among  mountaineers  have  always 
been  famed  as  fighting  men,  for  they  have  learned  endur- 
ance and  courage  from  the  severe  conditions  of  life  in 
their  rugged  homes.  Regiments  of  cavalry  recruited  from 
dwellers  on  grassy  plains  are  famous  as  "rough-riders," 
whether  they  are  Russian  Cossacks  or  American  cowboys ; 
their  skill  and  endurance  as  horsemen  are  a  natural  result 
of  habits  developed  in  an  open  country  of  large  distances, 
where  riding  is  as  appropriate  a  means  of  going  about  as 
walking  is  in  a  mountainous  district. 

What  example  can  you  give  of  a  people  whose  home  favored  their 
becoming  skillful  sailors,  and  who  thereby  became  invaders  and  con- 
querors of  other  lands?     (See  page  321.) 

The  fate  of  battle  fields  has  been  many  a  time  determined 
by  the  arrangement  of  high  and  low  ground;  hence  an 
intimate  knowledge  of  land  forms  and  of  local  geography 
is  of  great  importance  to  military  commanders.  During 
the  recent  war  in  South  Africa   the  Boers,  having  an 


370  ELEMENTARY  PHYSICAL  GEOGRAPHY 

accurate  acquaintance  with  their  country,  often  occupied 
the  crests  of  hills,  and  thus  gained  advantage  over  the 
British  soldiers,  who  had  to  make  attack  while  climbing  up 
a  slope  from  Tower  ground. 

What  can  you  learn  about  the  Spartans  at  Thermopylae  ?  What 
can  you  tell  of  Braddock's  defeat  ? 

209.  Geographical  Factors  favoring  the  Development  of 
Great  Britain.  —  The  progress  and  prosperity  of  a  nation 
are  even  more  dependent  in  peace  than  in  war  on  the 
advantage  that  its  people  have  learned  to  take  of  their 
surroundings. 

West  of  continental  Europe,  in  the  latitude  of  Labrador, 
there  is  an  island  whose  climate  is  remarkably  mild,  because 
it  is  on  the  leeward  side  of  an  ocean  across  which  the  sur- 
face waters  and  the  winds  move  obliquely  poleward  from 
warmer  latitudes.  The  island  is  therefore  fertile  and  has 
long  been  noted  for  its  agricultural  products.  The  narrow 
strait  by  which  it  is  separated  from  the  continent  has  served 
as  a  natural  fortification  against  the  armies  of  neighboring 
nations ;  nearly  a  thousand  years  have  passed  since  the 
island  has  been  successfully  invaded.  It  has  rich  mines  of 
coal  and  iron,  and  these  natural  products  have  been  skill- 
fully used  in  promoting  manufactures  of  the  most  diversi- 
fied kinds.  It  has  excellent  harbors,  and  many  of  its  people 
have  therefore  been  fishermen  and  sailors ;  its  navigators  have 
crossed  the  most  distant  oceans  and  have  developed  a  world- 
wide commerce.  As  the  population  of  the  island  increased 
under  all  these  favoring  conditions,  many  of  its  people 
emigrated  to  the  new  lands  discovered  by  its  explorers 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        371 

and  founded  colonies  in  them;  and  to-day  the  sun  never  sets 
on  the  island's  possessions.  The  empire  thus  established 
is  the  most  widespread  that  the  world  has  ever  seen. 

210.  The  United  States.  —  A  more  modern  instance  of 
the  dependence  of  prosperity  on  geographical  elements  is 
seen  in  the  rapid  growth,  as  a  world  power,  of  a  young 
nation  whose  center  of  population  now  lies  in  a  region 
where  the  winter  is  so  severe  that  provision  must  be  made 
for  it,  yet  where  the  summer  warms  a  fertile  soil  from 
which  industry  secures  provision  in  plenty  and  to  spare  ; 
where  open  plains  and  great  rivers  made  it  easy  for  new 
settlers  to  enter  the  country,  and  where  the  small  relief  of 
the  surface  favored  the  construction  of  the  numerous  rail- 
roads demanded  by  growing  traffic,  yet  where  the  variety 
of  form  is  sufficient  to  promote  diversified  industries;  where 
the  products  of  forest  and  mine  are  added  to  those  of  the 
farm,  and  where  these  excellent  conditions  are  spread  over 
so  extensive  an  area  that  abundant  opportunity  is  offered 
for  a  vast  population. 

Yet  these  favoring  conditions  have  not  been  in  them- 
selves sufficient  for  the  growth  of  a  powerful  nation.  The 
aboriginal  inhabitants  of  this  great  land  were  savages  who 
did  not  know  how  to  develop  its  riches.  The  entire 
territory  remained  a  wilderness  until  it  was  entered  by  the 
descendants  of  a  race  that  had,  by  long  occupation  of 
another  highly  favored  region,  gained  a  leading  position 
among  the  peoples  of  the  Old  World. 

But  these  members  of  the  leading  race  of  the  Old  World 
would  not  have  left  their  homes  for  a  new  country,  however 


372  ELEMENTARY  PHYSICAL  GEOGRAPHY 

favorable  its  geographical  features,  if  its  government 
had  been  tyrannical  and  oppressive.  It  is  therefore  not 
local  geographical  factors  alone  that  have  so  soon  given 
this  young  nation  a  giant's  strength,  but  three  highly 
favoring  conditions  combined:  a  land  well  situated,  of 
great  extent,  and  rich  in  many  forms  of  natural  wealth ; 
numerous  immigrants  from  the  leading  race  of  the  Old 
World;  and  a  liberal  form  of  government  under  which 
the  highest  opportunity  is  open  to  every  citizen.  Let  us 
remember  that  "  it  is  excellent  to  have  a  giant's  strength, 
but  tyrannous  to  use  it  like  a  giant." 

QUESTIONS 

Sec.  191.  How  have  geographical  conditions  affected  man's  prog- 
ress ?  Illustrate  this  by  the  use  that  has  been  made  of  the  winds ; 
of  waterfalls ;  of  flood  plains ;  of  terrestrial  magnetism ;  of  coal  and 
iron.  Give  some  examples  of  the  effects  of  geographical  conditions 
on  the  distribution  of  plants ;  of  animals ;  on  man's  way  of  living. 

192.  How  is  it  known  that  the  earth  has  long  been  inhabited  ? 
What  barriers  prevent  the  spread  of  organic  forms  ?  Contrast  the 
spreading  of  plants  having  heavy  and  light  seeds.  In  what  way  do 
corals  and  mussels  resemble  certain  land  plants?  How  have  free- 
moving  animals  been  distributed?  Contrast  the  distribution  of 
walking  and  of  flying  birds.  How  is  the  rotation  of  the  earth 
shown  to  be  a  factor  in  the  distribution  of  certain  birds? 

193.  How  is  the  number  of  plants  or  animals  in  a  region  limited  ? 
How  does  man  sometimes  cause  a  change  in  these  numbers  ?  Why 
do  plants  and  animals  tend  to  increase  in  number?  Why  does 
their  number  not  increase?  Explain  the  phrases  "struggle  for 
existence  "  ;  "  survival  of  the  fittest " ;  "  natural  selection."  Upon 
what  does  the  chance  of  survival  depend  ?  Illustrate  by  examples 
from  sea  animals.     What  effects  follow  from  the  illumination  of 


THE  DISTRIBUTION  OF  ORGANIC  FORMS        373 

the  earth  from  the  sky  ?     Give  some  examples  of  protection  gained 
by  living  in  out-of-the-way  places. 

194.  Compare  ancient  and  modem  plants  and  animals.  How 
have  variations  in  plants  and  animals  been  caused?  Illustrate  by 
changes  in  a  coastal  plain  ;  in  mountains ;  in  climate. 

195.  Name  one  of  the  strongest  contrasts  of  geographical  con- 
ditions. What  proof  can  be  given  of  the  great  age  of  the  continents 
and  oceans  ?  What  consequences  follow  from  the  greater  density  of 
water  than  of  air?  Contrast  the  conditions  of  the  sea  bottom  with 
those  of  the  lands.  State  some  results  of  these  contrasted  conditions. 
What  can  you  tell  about  the  warm-blooded  animals  of  the  sea? 
Why  are  they  believed  to  be  descended  from  land  animals?  Give 
examples  of  the  remarkable  instincts  of  certain  land  animals. 

196.  How  are  the  several  continents  arranged  ?  Over  what  region 
are  similar  land  plants  and  animals  found  ?  Name  some  examples. 
Name  some  of  the  animals  and  plants  of  the  lower  northern  lati- 
tudes in  the  Old  and  in  the  New  Worlds.  What  is  inferred  from 
their  differences  ?  Name  some  of  the  animals  of  the  three  southern 
continents.  Why  are  mammals  not  found  in  Australia  ?  Name  some 
animals  and  plants  native  to  one  part  of  the  world  and  thriving  in 
another  part. 

197.  How  has  mankind  been  divided  into  races?  In  what  ways 
do  the  races  differ?  Describe  the  races  of  Eurasia;  of  America; 
of  Africa ;  of  Australia.     How  are  the  races  now  distributed  ? 

198.  What  forms  of  life  are  found  on  continental  islands  ?  Wliat 
is  inferred  from  this  ?  How  have  these  islands  been  separated  from 
the  mainland?  Illustrate  by  the  cassowaries;  by  mammals  and 
marsupials  on  the  islands  between  Asia  and  Australia.  What  forms 
are  found  on  oceanic  islands?  What  is  the  origin  of  the  names 
Azores  and  Galapagos? 

199.  How  does  climate  control  the  distribution  of  plants  ?  Illus- 
trate by  the  palm  (see  Figure  112),  by  cotton,  corn,  and  wheat.  What 
is  the  vegetation  of  the  northern  treeless  belt?  How  does  climate 
control  the  distribution  of  animals  ?    Give  examples.     How  does  the 


374  ELEMENTARY  PHYSICAL  GEOGRAPHY 

distribution  of  plants  control  that  of  animals  ?    Give  examples  from 
North  and  South  America. 

200.  Name  some  direct  and  some  indirect  effects  of  climate  on 
man.  Why  are  climatic  influences  more  apparent  on  savage  tribes 
than  on  civilized  peoples?  Describe  the  conditions  prevailing  in 
the  forests  of  equatorial  Africa.  Describe  the  life  of  the  Dwarfs  of 
these  forests.  Explain  the  relation  between  their  life  and  their 
environment.  Do  the  same  for  Greenland  and  the  Eskimos.  What 
general  truth  do  these  examples  illustrate  ? 

201.  Give  an  example  of  the  effects  of  the  change  of  seasons  on 
plants  in  the  torrid  zone ;  in  the  north  temperate  zone.  What  are 
annual  plants?  Name  several  ways  in  which  animals  survive  the 
winter.  How  does  the  oblique  position  of  the  earth's  axis  affect  the 
life  of  plants  and  animals?  How  does  change  of  season  affect  man's 
way  of  living  ?  Give  examples  from  the  Caspian  steppes ;  from 
Algeria.  Of  what  advantage  has  winter  been  in  the  development 
of  civilization? 

202.  How  does  climate  vary  on  mountains  ?  Describe  the  changes 
of  vegetation  seen  on  ascending  a  mountain.  What  is  the  tree  line  ? 
the  snow  line  ?  What  are  Alpine  plants  ?  In  what  lowland  region 
are  the  plants  of  high  mountains  found?  What  may  be  learned 
from  the  distribution  of  the  ibex?  Give  a  similar  example  from 
the  mountains  of  New  England. 

203.  How  have  mountain  valleys  been  used  by  defeated  peoples? 
Give  an  example  from  the  Pyrenees ;  from  the  Caucasus.  Why  is 
life  more  difficult  in  mountains  than  on  plains  ?  Name  some  of  the 
customs  of  mountaineers. 

204.  Mention  some  of  the  features  of  desert  vegetation.  What 
is  the  effect  of  rain  in  a  desert  ?  Describe  the  conditions  of  growth 
of  desert  plants.     What  can  you  say  of  desert  animals  ? 

205.  Describe  the  inhabitants  of  deserts ;  the  conditions  of  life 
in  the  Sahara ;  the  Indians  of  the  Sonoran  region. 

206.  What  are  oases?  What  controls  their  location ?  Why  are 
deserts   barren?     Describe  the  oasis  of  Siwa.     Describe  the  Nile 


THE  DISTRIBUTION  OF  ORGANIC  FORMS         375 

valley.    To  what  are  its  floods  due  ?    Of  what  value  are  they  ?    How 
is  their  value  to  be  increased? 

207.  AVhere  are  the  simplest  examples  of  the  relation  of  man 
and  nature  found?  Why  are  civilized  people  less  dependent  than 
savages  on  natural  conditions?  How  have  civilized  people  been 
affected  by  geographical  conditions?  Give  examples.  What  are 
anchor  draggers?  Show  that  savages  are  dependent  on  immediate 
surroundings  and  on  individual  work.  Show  that  civilized  people 
are  often  dependent  on  distant  supplies  and  on  the  work  of  many 
men  in  many  trades. 

208.  What  geographical  factors  have  affected  the  historical 
development  of  North  America?  How  were  the  boundaries  of  the 
smaller  northeastern  states  determined?  Show  that  the  character 
of  soldiers  and  their  success  in  warfare  are  dependent  on  geographical 
conditions. 

209.  210.  Describe  the  geographical  factors  that  have  favored 
the  development  of  Great  Britain.  What  favorable  factors  are 
found  in  the  United  States  ?  What  other  factors  have  contributed 
to  our  national  growth  ? 


APPENDIX 


REFERENCES  FOR  SUPPLEMENTARY  READING 

The  titles  in  the  following  list  have  been  selected  with  especial 
reference  to  their  accessibility  in  public  libraries.  Mention  is  made 
of  the  publications  of  the  U.  S.  Geological  Survey  because  of  their 
great  value  to  the  geographer  as  well  as  of  their  wide  distribution. 
Numbers  preceding  certain  references  indicate  the  page  of  this  book 
to  which  the  articles  cited  pertain. 

GENERAL  REFERENCES 

Gannett,  The  United  States,  Stanford's  Compendium  of  Geography, 
Edward  Stanford,  1898. 

The  International  Geography.     D.  Appleton  &  Co.,  1899. 

Annual  Reports,  Bulletins,  Monographs,  and  Geological  Folios  of 
the  U.  S.  Geological  Survey.  Some  of  the  more  geographical 
essays  are  referred  to  below  (abbrev.,  G.  S.  Ann.  Rep.,  etc.). 

The  following  geographical  periodicals  contain  much  material 
serviceable  in  teaching: 

National  Geographic  Magazine,  Washington,  D.  C.  (abbrev.,  N.  G.  M.). 
Bulletin  of  the  American  Geographical  Society,  New  York  (B.  A.  G.  S.). 
Journal  of  School  Geography,  Lancaster,  Pa.  (J.  S.  G.). 
Bulletin  of   the  American  Bureau  of  Geography,  AVinona,  Minn. 
(B.  A.  B.  G.). 

(The  two  preceding  periodicals  are  united,  since  January,  1902,  under  the 
title,  The  Journal  of  Geography .) 

Geographical  Journal,  London  (G.  J.).    . 
Scottish  Geographical  Magazine,  Edinburgh  (S.  G.  M.). 

377 


378  ELEMENTARY  PHYSICAL  GEOGRAPHY 

Platt,  The  Better  Books  in  School  Geography,  J.  S.  G.,  II,  '98,  181. 

(All  the  books  mentioned  in  the  above  article  would  be  found  serviceable 
in  school  libraries.) 

Mill,  Hints  to  Teachers  and  Students  on  the  Choice  of  Geographical 

Books.     Longmans,  Green  &  Co. 
Davis,  The  Equipment  of  a  Geographical  Laboratory,  J.  S.  G.,  IT, 

'98,  170. 
Cornish,  Laboratory  Work  in  Elementary  Physiography,  J.  S.  G., 

I,  '97,  172,  204. 
National    Geographic    Monographs,    American    Book    Co.,    1895 

(N.  G.  Mon.). 
Preliminary  Report  of  Committee  on  Physical  Geography  of  N.  E.  A. ; 

J.  S.  G.,  II,  '98,  248. 

CHAPTER  I.     THE  EARTH  AS   A  GLOBE 

Young,  Astronomy.     Ginn  &  Company,  1888. 

Todd,  Astronomy.     American  Book  Co.,  1897. 

ScHOTT,  The  Earth's  Shape  and  Size,  N.  G.  M.,  XII,  '01,  36. 

CHAPTER  II,     THE  ATMOSPHERE 

Waldo,  Elementary  Meteorology.     American  Book  Co.,  1896. 

Davis,  Elementary  Meteorology.     Ginn  &  Company,  1894. 

Jameson,  Elementary  Meteorology,  J.  S.  G.,  II,  '98,  2. 

Greely,  American  Weather.     Dodd,  Mead  &  Co.,  1888. 

Ward,  Practical  Exercises  in  Elementary  Meteorology.     Ginn  & 

Company,  1899. 
Ward,  Equipment  of  a  Meteorological  Laboratory,  J.  S.  G.,  Ill, 

'99,  241. 
Bartholomew,  Physical  Atlas,  Yol.  Ill,  Meteorology.     Lippincott. 

PAGE 

63.  Illustrated  Cloud  Forms,  U.  S.  Hydrographic  Office,  Washing- 
ton, D.C. 

67.  Garriott,  West  Indian  Hurricanes,  X.  G.  M.,  X,  '99,  17,  343 ; 
XI,  '00,  384. 


APPENDIX  379 

PAOK 

72.   Greely,  Rainfall  Types  of  the  United  States,  N.  G.  M.,  V, 

'93,  45. 
72.    Harrington,  Rainfall   of  the  United  States,  U.  S.  Weather 

Bureau,  Bulletin  C,  1894. 
72.    Gannett,  Redwood  Forest  of  the  Pacific  Coast,  N.  G.  M.,  X, 

'99,  145. 
84.   Davis,  The  Temperate  Zones,  J.  S.  G.,  I,  '97,  139.. 
84.   Ward,  Climatic  Control  of  Occupations  in  Chile,  J.  S.  G.,  I, 

'97,  289. 
87.   Davis,  Practical  Exercises  in  Geography,  N.  G.  M.,  XI,  '00,  62. 


CHAPTER  III.     THE  OCEAN 

Thomson,  The  Depths  of  the  Sea.     Macmillan  &  Co.,  1874. 
Thomson,  The  Voyage  of  the  Challenger :  The  Atlantic.     Macmillan 

&  Co.,  1877. 
SiGSBEE,  Deep  Sea  Sounding  and  Dredging,  Washington,  1880. 
Tanner,  Deep  Sea  Exploration,  U.  S.  Fish  Commission,Washington. 
Agassiz,  Three  Cruises  of  the  Blake,  Cambridge,  1888. 
Monthly  Pilot  Charts  of  the  North  Atlantic  and  the  North  Pacific 

Oceans,  U.  S.  Hydrographic  Office,  Washington. 
Semple,  The  Atlantic  and  Pacific  Oceans,  J.  S.  G.,  Ill,  '99, 121, 172. 

PAGE 

109.   Davis,  Waves  and  Tides,  J.  S.  G.,  II,  '98,  122. 

113.  Scidmore,  Earthquake  Wave,  Japan,  N.  G.  M.,  VII,  *95,  285. 

114.  Davis,  Winds  and  Ocean  Currents,  S.  G.  M.,  XIII,  '97,  55, 

and  J.  S.  G.,  II,  '98,  16; 

118.  PiLLSBURY,  The  Gulf  Stream,  Ann.  Rep.  U.  S.  Coast  Survey, 

1890. 

119.  Tide  Tables,  published  annually  by  U.  S.  Coast  Survey. 

121.   Jefferson,  Atlantic  Estuarine  Tides,  N.  G.  M.,  IX,  '98,  400  : 
also  497. 


380  ELEMENTARY  PHYSICAL  GEOGRAPHY 


CHAPTER  IV.     THE  LANDS 

Shaler,  Aspects  of  the  Earth.     Charles  Scribner's  Sons,  1889. 

J.  Geikie,  Earth  Sculpture.     G.  P.  Putnam's  Sons. 

Text-books    on    Elementary   Geology,    by   Dana,   Geikie,    Leconte, 

Scott,  Tarr,  and  Brigjiam. 
Shaler,  Origin  and  Nature  of  Soils,  G.  S.  12th  Ann.  Rep.,  Pt.  I,  219. 
Patterson,  Work  of  the  Water  Giant,  J.  S.  G.,  Ill,  '99,  5. 


CHAPTER  V.  PLAINS  AND  PLATEAUS 

PAGE 

142.  Davis,  Description  of  the  Harvard  Geographical  Models,  pub- 
lished by  the  Boston  Society  of  Natural  History,  Berkeley 
Street,  Boston,  Figures  60,  62,  and  104  are  taken  from 
these  models. 

148.  Glenn,  South  Carolina,  J.  S.  G.,  II,  '98,  9,  85. 

149.  Cobb,  North  Carolina,  J.  S.  G.,  I,  '97,  256,  300. 
156.    Abbe,  Maryland,  B.  A.  B.  G.,  I,  '00,  151,  242. 

156.  McGee,  Chesapeake  Bay,  G.  S.  7th  Ann.  Rep.,  548. 

157.  McGee  (Fall  Line),  G.  S.  12th  Ann.  Rep.,  360. 

158.  Hatcher,  Patagonia,  N.  G.  M.,  XI,  '00,  41. 

158.  Johnson,  High  Plains,  N.  G.  M.,  IX,  '98,  493  ;  G.  S.  21st  Ann. 

Rep.,  601. 

159.  Fenneman,  Climate  of  the  Great  Plains,  J.  S.  G.,  Ill,  '99, 1,  46. 
161.  Collie,  Physiography  of  Wisconsin,  B.  A.  B.  G.,  II,  '01,  270. 
166.    Powell,   Exploration    of   the    Colorado  River  of   the   West, 

Washington,  1875.     See  pp.  98-102,  130,  131. 

166.  Powell,  Canyons  of  the  Colorado.  Flood  &  Vincent,  Mead- 
ville.  Pa. 

166.  DuTTON,  Colorado  Canyon,  G.  S.  2d  Ann.  Rep.,  4-9  ;  G.  S. 
Monogr.  II. 

168.  Campbell  and  Mendenhall  (Plateau  of  West  Virginia), 
G.  S.  17th  Ann.  Rep.,  480. 

168.  Roosevelt,  Winning  of  the  West,  I,  101 ;  III,  13.  G.  P.  Put- 
nam's Sons,  1894. 


APPENDIX  381 

PAOK 

168.    Semple,  Influence  of  the  Appalachian  Barrier  upon  Colonial 

History,  J.  S.  G.,  I,  '97,  33. 
172.    Hodge,  The  Enchanted  Mesa,  N.  G.  M.,  VIII,  '97,  273. 

CHAPTER  VI.     MOUNTAINS 

178.    Russell,  Southern  Oregon,  G.  S.  4th  Ann.  Rep.,  435. 

181.   Russell,  Mountains  of  Nevada,  G.  S.  Mouogr.  XI,  38. 

185.   Fay,  Canadian  Alps,  J.  S.  G.,  I,  '97,  160. 

185.  WiLLCOX,  Canadian  Rockies,  J.  S.  G.,  I,  '97,  293  ;  also  N.  G.  M., 
X,  '99,  113. 

197.  Lubbock,  Scenery  of  Switzerland.  Macmillan  &  Co.,  1896 
(p.  124). 

201.   Milne,  Earthquakes.     D.  Appleton  &  Co.,  1883. 

205.    Willis,  Round  about  AsheviUe,  N.C.,  N.  G.  M.,  I,  '89,  291. 

205.  A.  Geikie,  Scenery  of  Scotland,  2d  ed.  (chapters  on  High- 
lands).    Macmillan  &  Co.,  1887. 

205.  Herbertson,  Geography  of  Scotland,  J.  S.  G.,  II,  '98,  161. 

206.  McGee,    Geographical    History    of    the    Piedmont    Plateau, 

N.  G.  M.,  VII,  '96,  261. 
206.   Keith,  Piedmont  Plateau,  G.  S.  14th  Ann.  Rep.,  366. 
208.    Davis,  Southern  New  England,  N.  G.  Mon. 
208.   Davis,  Geographical  Illustrations  (Southern  New  England), 

published  by  Harvard  University,  Cambridge,  Mass. 
210.   Willis,     Northern    Appalachians,    N.    G.   Mori.      See    also 

B.  A.  B.  G.,  I,  '00,  342-355. 
210.   Hayes,  Southern  Appalachians,  N.  G.  Mon. 
210.   Hayes,  Physiography  of  the  Chattanooga  District,  G.  S.  19th 

Ann.  Rep.,  Pt.  H,  1. 
210.   Davis,  Rivers  and  Valleys  of  Pennsylvania,  N.  G.  M.,  I,  183. 

CHAPTER  VII.     VOLCANOES 

Russell,  Volcanoes  of  North  America.     Macmillan,  1897. 
Dana,  Characteristics  of  Volcanoes.     Dodd,  Mead  &  Co.,  1890. 


382  ELEMENTARY  PHYSICAL  GEOGRAPHY 

JuDD,  Volcanoes.     D.  Appleton  &  Co.,  1881. 
Dodge,  Volcanoes,  J.  S.  G.,  I,  '97,  179  ;  IV,  '00,  350. 

PAOB 

218.  Lyell,  Principles  of  Geology  (Monte  Nuovo,  I,  607;  JoruUo, 

I,  585).     D.  Appleton  &  Co.,  1872. 

219.  DiLLER,  A  Late  Volcanic  Eruption  in  Northern  California, 

G.  S.  Bull.  No.  79. 
221.   Phillips,  Vesuvius.     Macmillan  &  Co.,  1869. 

221.  Milne,  Earthquakes.     D.  Appleton  &  Co.,  1883. 

222.  DiLLER,  Crater  Lake,  N.  G.  M.,  VIH,  33. 
222.    DiLLER,  Crater  Lake,  J.  S.  G.,  I,  '97,  266. 

226.  Moore,  The  Active  Volcanoes  North  of  Kivu  (Central  Africa), 

G.  J.,  XVIT,  '01,  11. 

227.  DuTTON  (Lava  Flows),  G.  S.  Monogr.  II. 

227.    DuTTON,  Hawaiian  Volcanoes,  G.  S.  4th  Ann.  Rep.,  "81. 
229.    DiLLER,  Mt.  Shasta,  N.  G.  Mon.    See  also  B.  A.  B.  G.,  I,  '00, 260. 
231.    Hayes,  Physiography  of  the  Nicaragua  Canal  Route,  N.  G.  M., 
X,  '99,  233. 


CHAPTER  VIII.     RIVERS  AND  VALLEYS 
Russell,  Rivers  of  North  America.    G.  P.  Putnam's  Sons,  1898. 

PAGE 

235.    HovEY,  Celebrated  American  Caverns.    Clarke,  Cincinnati. 

235.  HovEY,  Mammoth  Cave,  J.  S.  G.,  I,  '97,  133. 

236.  Walcott,  Natural  Bridge  of  Virginia,  N.  G.  M.,  V,  '93,  59. 

238.  Chamberlin,  Artesian  Wells,  G.  S.  5th  Ann.  Rep.,  125. 

239.  Weed,  Hot  Springs,  G.  S.  9th  Ann.  Rep.,  613. 
247.  Bell,  The  Labrador  Peninsula,  S.  G.  M.,  XI,  335. 
251.  Gilbert,  Niagara,  N.  G.  Mon. 

260.   Davis,  Seine,  Meuse,  and  Moselle,  N.  G.  M.,  VII,  '97,  189,  228. 
264.   Gannett,  The  Flood  of  April,  1897,  in  the  Lower  Mississippi, 

S.  G.  M.,  XIII,  '97,  419. 
266.   Fairbanks,  Physiography  of  California,  B.  A.  B.  G.,  II,  '01, 

232,  329. 


APPENDIX  383 


CHAPTER  IX.     DESERTS  AND  GLACIERS 

I'AOE 

•J78.  Marbut,  Missouri,  J.  S.  G.,  I,  '97,  110,  144. 

280.  Plati,  The  Sahara,  J.  S.  G.,  IV,  '00,  255. 

282.  King,  Geological  Survey,  40th  Parallel,  Washington,  I,  4G0, 

484  ;  II,  470. 

282.  McGee,  Seriland,  N.  G.  M.,  VII,  '97,  125. 

284.  Russell,  Past  and  Present  Lakes  of  Nevada,  N.  G.  Mon. 

286.  Davis,  A  Temporary  Sahara,  J.  S.  G.,  IV,  '00,  171. 

288.  Gilbert,  Lake  Bonneville,  G.  S.  2d  Ann.  Rep.,  1C9. 

288.  Gilbert,  Lake  Bonneville,  G.  S.  Monogr.  I. 

289.  Russell,  Lake  Lahontan,  G.  S.  3d  Ann.  Rep.,  195. 

290.  Holder,  A  Remarkable  Salt  Deposit,  N.  G.  M.,  XII,  '01,  391. 
290.  Russell,  Glaciers  of  North  America.  Ginn  &  Company,  1897. 
290.  Shaler  and  Davis,  Glaciers.  Houghton,  Mifflin  &  Co.,  1881. 
290.  Tyndall,  Forms  of  Water.     D.  Appleton  &  Co.,  1872. 

290.   J.  Geikie,  Great  Ice  Age,  3d  ed.    D.  Appleton  &  Co.,  1895. 

290.  Wright,  Ice  Age  in  North  America.    D.  Appleton  &  Co.,  1890. 

291.  Arctowski,  Exploration  of  Antarctic  Lands,   G.  J.,  XVII, 

'01,  50. 
291.   Nansen,   First   Crossing   of    Greenland,    1890.      Longmans, 
Green  &  Co.,  1890. 

291.  Peary,  Northward  over  the  Great  Ice.     Frederick  A.  Stokes 

Co.,  1898. 

292.  Russell,  Glaciers  of  Alaska,  G.  S.  13th  Ann.  Rep.,  7. 
292.   Russell,  Mt.  St.  Elias,  Alaska,  N.  G.  M.,  Ill,  53. 
292.    Reid,  Muir  Glacier,  Alaska,  N.  G.  M.,  IV,  19. 

292.    Reid,  Glacier  Bay  and  its  Glaciers,  G.  S.  16th  Ann.  Rep.,  Pt.  I, 

415. 
292.   Russell,  Existing  Glaciers  of  the  United  States,  G.  S.  5th 

Ann.  Rep.,  303. 
295.   Russell,  Mono  Lake  Region,  G.  S.  8th  Ann.  Rep.,  Pt.  T,  321. 
295.    Bell,  The  Labrador  Peninsula,  S.  G.  M.,  XI,  335. 
295.   A.  Geikie,  Scenery  of  Scotland,  2d  ed.  (chapters  on  Glacial 

Action).     Macmillan  &  Co.,  1887. 


384  ELEMENTARY  PHYSICAL  GEOGRAPHY 

PAGE 

295.  Russell,  Geography  of  the  Laurentian  Basin,  B.  A.  G.  S., 

XXX,  '98,  226. 

296.  McGee,  Drift  Plains  of  Iowa,  G.  S.  11th  Ann.  Rep.,  393. 
296.   Taylor,  Studies  in  Indiana  Geography,  Terre  Haute,  1897. 

("Short  History  of  the  Great  Lakes.") 

296.  Gilbert,  Modification  of  Great  Lakes  by  Earth  Movement, 

N.  G.  M.,  VIII,  233. 

297.  Chamberlin,  Rock  Scorings,  G.  S.  7th  Ann.  Rep.,  155. 
297.    Chamberlin,  Terminal  Moraines,  G.  S.  3d  Ann.  Rep.,  295. 
297.    Todd,  Terminal  Moraines  in  Dakota,  G.  S.  BuU.  No.  144, 

16. 
297.   Dryer,  Studies  in  Indiana  Geography,  Terre  Haute,   1897. 

The  Morainic.  Lakes  of  Indiana. 
297.   Leverett,  The  lUinois  Glacial  Lobe,  G.  S.  Mon.,  XXXVIII. 

299.  Upham,  Glacial  Lake  Agassiz,  G.  S.  Monogr.  XXV. 

300.  Gannett,  Lake  Chelan,  N.  G.  M.,  IX,  '98,  417. 

300.    Tarr,  Lakes  and  Swamps  of  New  York,  B.  A.  G.  S.,  XXXI, 
'99,  1. 


CHAPTER  X.     SHORE  LINES 

304.  Shaler,  Sea  and  Land.     Charles  Scribner's  Sons,  1894. 

308.  Shaler,  Seacoast  Swamps  of  Eastern  United  States,  G.  S. 

6th  Ann.  Rep.,  93. 

308.  Shaler,  Beaches  and  Tidal  Marshes,  N.  G.  Mon. 

310.  Gilbert,  Features  of  Lake  Shores,  G.  S.  5th  Ann.  Rep.,  75. 

311.  Shaler,  Natural  History  of  Harbors,  G.  S.  13th  Ann.  Rep.,  93. 
317.  A.  Geikie,  Scenery  of   Scotland,  2d  ed.    (chapter  on  Shore 

Features).     Macmillan  &  Co.,  1887. 
324.   Darwin,  Coral  Reefs.     D.  Appleton  &  Co.,  1889. 
324.    Dana,  Corals  and  Coral  Islands.     Dodd,  Mead  &  Co.,  1890. 
324.   A.  Agassiz,  Letter  in  Am.  Journ,  Science,  Feb.,  1898. 


APPENDIX  386 


CHAPTER  XI.     DISTRIBUTION  OF  PLANTS,  ANIMALS, 
AND  MAN 

PAGE 

333.  Heilprin,  Distribution  of  Animals.    D.  Appleton  &  Co.,  1886. 

333.  Beddard,  Zoogeography.    University  Press,  Cambridge,  1895. 

333.  MacMillan,  Geographical  Distribution  of  Plants,  J.  S.  G., 
April,  '97. 

345.  Brinton,  Races  and  Peoples. 

346.  Wallace,  Island  Life.     Macmillan  &  Co.,  1891. 

347.  Wallace,  Travels  in  the   Malay   Archipelago,      Macmillan 

&  Co.,  9th  ed. 

348.  Merriam,  Geographical  Distribution  of  Terrestrial  Animals 

and  Plants,  N.  G.  M.,  VI,  229. 
355.    Gannett,  The  Timber  Line,  B.  A.  G.  S.,  XXXI,  '99,  118. 
363.   Jennings-Bra'mley,  A  Journey  to  Siwa,  G.  J.,  X,  '97,  597. 


386  ELEMENTARY  PHYSICAL  GEOGRAPHY 


KEFERENCES  FOR  MAPS 

The  following  list  of  map  sheets,  selected  chiefly  from  those  pub- 
lished by  the  U.  S.  Geological  Survey  and  the  U.  S.  Coast  and  Geo- 
detic Survey,  will  be  found  of  service  in  illustrating  various  examples 
of  land  forms  referred  to  in  Chapters  V  to  X.  Complete  lists  of  maps 
published  by  these  Surveys  can  be  had,  free  of  charge,  on  application. 
The  sheets  here  named  might  be  supplemented  by  many  others  in 
illustration  of  special  localities.  Some  account  of  the  cost  and  of  the 
method  of  ordering  and  using  the  maps  is  given  in  the  Journal  of 
School  Geography,  September,  1897,  and  October,  1898.  Coast  Sur- 
vey maps  are  here  marked  "  C.  S."  The  others,  unless  specially  des- 
ignated, are  published  by  the  Geological  Survey.  Numbers  preceding 
the  names  indicate  the  pages  of  this  book  to  which  the  maps  refer. 

CHAPTER  V.  PLAINS  AND  PLATEAUS 

PAGE 

152.   Relief  Map  of  New  Jersey,  published  by  the  State  Geological 

Survey,  Trenton,  N.J.;  price,  25  cents. 
154.   Nomini,  Md. 
159.   Topographic  Atlas  of  the  United  States,  folio  1,  Physiographic 

Types,  Pis.  I-III. 
164.    Mt.  Trumbull,  Diamond  Creek,  Ariz. 
168.    Kanawha  Falls,  Nicholas,  W.  Va. 
172.    Watrous,  Corazon,  N.M.;  Abilene,  Brownwood,  Tex. 
174.    Mt.  Trumbull,  Kaibab,  Echo  Cliffs,  Ariz. 

CHAPTER  VI.     MOUNTAINS 

181.    Disaster,  Nev. ;  Alturas,  Cal. 
186.    Platte  Canyon,  Huerfano  Park,  Col. 
204.    Asheville,  Mt.  Mitchell,  Pisgah,  N.C. 

207.    Atlanta,  Ga.     (Stone  mountain  is  a  fine  example  of  a  monad- 
nock  on  the  uplands  of  Georgia.) 


APPENDIX  387 

PAGE 

208.    Chesterfield,   Granville,   Mass.;    Winsted,   Derby,   Bridgeport, 
Conn. 

210.  Harrisburg,  Hummelstown,  Lykens,  Pa. 

211.  C.  S.  No.  710. 


CHAPTER  VII.     VOLCANOES 

222.    Crater  Lake  (special  sheet),  Oregon. 

230.    Shasta,  Cal. ;  San  Francisco  Mountain,  Ariz. 


CHAPTER  VIII.     RIVERS   AND  VALLEYS 

247.    Citra,  Fla. 

251.   Niagara  Falls  (special  map). 

256.   Mesa  de  Maya,  Col. 

261.   Donaldsonville,  La. 

264.   8-Sheet  Map  of  the  Alluvial  Valley  of  the  Mississippi  River, 

published  by  the  Mississippi  River  Commission,  St.  Louis,  Mo. 
264.    Preliminary  Maps  of  the  Mississippi  River,  published  by  the 

Mississippi  River  Commission,  St.  Louis,  Mo.     Edition  of 

1900. 
268.    C.  S.  No.  194,  Mississippi  Delta. 
271.   Versailles,  Tuscumbia,  Mo. 
273.   Delaware  Water  Gap,  Pa. ;  Harpers  Ferry,  Va. 


CHAPTER   IX.     DESERTS  AND  GLACIERS 

281.  Disaster,  Granite  Range,  Long  Valley,  Nev. 

299.  Oconomowoc,  Siln  Prairie,  Wis. 

301.  Elizabethtown,  Mt.  Marcy,  N.Y. 

302.  Rochester,  N.Y. ;  Minneapolis,  Minn. 


388  ELEMENTARY  PHYSICAL  GEOGRAPHY 

CHAPTER  X.     SHORE  LINES 

PAOB 

308.  C.  S.  Nos.  121,  122,  123  (New  Jersey  coast). 

311.  C.  S.  Nos.  103,  104,  105  (Maine  coast).  • 

313.  C.  S.  Nos.  108,  109  (Massachusetts  coast). 

316.  C.  S.  No.  674  (California  coast). 

322.  C.  S.  Nos.  8100,  706  (Alaska  coast). 

323.  C.  S.  No.  21  (Texas  coast). 


INDEX 


Adirondacks,  301. 

Africa,  55,  325,  343,  346,  360. 

Agriculture,  43,  62,  169,  230,  297, 

330,  354,  364,  370,  371. 
and  irrigation,   66,    71,    169, 

362. 
and  soil,  160,  206,  269,  278, 

287,  296,  363.       ' 
Air,  15,  23,  24,  see  Atmosphere. 
Alabama,  167. 

Alaska,  119,  212,  292,  299,  316. 
Allegheny  mountains,  210,  273. 

plateau,  167,  243,  256,  271. 

Alluvial  fans,  see  Fans. 
Alps,  185,  192,  203,  261,  299. 

glaciers  of,  292,  295. 

Amazon,  41,  66,  121. 
Andes,  27,  41,  189,  190,  231. 
Anemometer,  38. 
Animals,  in  caves,  236. 

and  climate,  336. 

on  deserts,  360. 

distribution,  332,  348.      • 

on  islands,  330,  346. 

on.  mountains,  26,  169,  365. 

in  ocean,  100,  105,  122,  124, 

338. 
Antarctic  ocean,  96,  104,  116. 

regions,  96,  129,  291.' 

Anticyclones,  46,  75,  77,  78,  80. 
Aphelion,  12. 


Appalachian  mountains,  239,  369. 
Arctic  ocean,  96,  116,  130. 

regions,  103,  336,  342. 

Argentina,  139,  190. 

Arid  regions,  180,  280,  see  Deserts. 

Aristotle,  2. 

Arizona,  climate,  71,  74. 

—  plateaus,  165,  172,  227. 

volcanoes,  226,  230. 

Artesian  wells,  238. 

Asia,  129,  343,  345,  346. 

Atlantic  ocean,   80,   84,   96,    100, 

104,  115,  130,  226,  367. 
Atmosphere,  23. 

circulation,  36,  40,  59,  304. 

color,  27,  76,  225. 

composition,  24. 

convection,  36,  60,  63. 

currents,  36,  62,  67. 

density,  26,  27. 

elasticity,  26. 

height,  15,  23. 

humidity,  60. 

pressure,  24,  90. 

properties,  15,  23,  29. 

saturation,  61,  63,  64. 

weight,  26. 

Atolls,  328,  see  Reefs. 
Augusta,  158. 
Aurora,  18. 
Australasia,  131,  346. 


390 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Australia,  50,  56,  71,  130,  343,  346. 
Avalanches,  192. 
Azores,  348. 

Bad  lands,  283. 

Baltimore,  156. 

Banks,  109. 

Barometer,  25^ 

Barriers,  167,  170,  189,  256,  333. 

Baselevel,  145,  255. 

Basin,  interior,  283,  288. 

river,  241. 

rock,  296,  300,  see  Lakes. 

waste-filled,  284,  see  Waste. 

Basques,  357. 

Bays,  119,  121,  156,  211,  314. 

Beach,  112,  307,  308,  313,  320. 

Beavers,  341. 

Bench,  200,  312,  327. 

Bengal,  Bay  of,  69,  72,  268. 

Bering  Strait,  130. 

Birds,  52,  334,  339,  341,  354. 

Black  mountains,  301. 

Blizzard,  78,  81. 

Blue  Ridge,  205. 

Bluff,  308,  see  Cliff. 

Boers,  369. 

Bolivia,  290. 

Bore,  121. 

Boundaries,  11,  190,  368. 

Bowlders,  298. 

Brahmaputra,  268. 

Brazil,  41,  68,  325,  366. 

Brickfielders,  81. 

Bristol  channel,  121. 

British  Columbia,  84,  212. 

British  Isles,  107,  119,  370. 

Buenos  Aires,  307. 

Buffaloes,  160. 


Buran,  81. 
Butte,  171. 

Cairo,  263,  363. 

Caldera,  221. 

California,  climate,  55,  71,  73. 

coast,  143,  314. 

fans,  267. 

moraines,  295. 

mountains,  178,  181. 

valley,  265,  266. 

volcanoes,  219. 

Calms,  43,  44,  54,  56,  57. 

Camden,  158. 

Camel,  248,  360. 

Canada,    85,    133,    255,    292,   295, 

300,  302. 
Canals,  232,  248,  320. 
Canoes,  248,  322,  352. 
Canyons,  162,  164,  166,  282. 
Cape  Cod,  138. 
<:!ape  Horn,  81,  118,  191. 
Cape  of  Good  Hope,  81,  118. 
Carbon,  24. 
Carbonic  dioxide,  24. 
Cardinal  points,  7. 
Caribbean  sea,  106. 
Caribou,  342. 
Cascade  mountains,  73. 
Cassowary,  347. 
Catskill  mountains,  167. 
Caucasus,  185,  292. 
Caverns,  235. 

Central  America,  106,  226,*  231. 
Ceylon,  83. 
Charleston,  158,  238. 
Chesapeake  bay,  156,  238,  368. 
Chicago,  369. 
Chile,  56,  190,  280. 


INDEX 


391 


China,  189,  269,  287,  345. 

Chinese,  345,  346. 

Chinook  wind,  189. 

Cinder  cone,  219. 

Circles,  9. 

Cirrus,  63. 

Cities,  156,  157,  158,  209,  263,  270, 

297,  302,  368. 
Civilization,  4,  84,  139,  170,  332, 

345,  355,  364,  370,  371. 
Clay,  139,  162,  366. 
Cleopatra's  Needle,  135. 
Cliff  dwellers,  167. 
Cliffs,  163,  166,  167,  171,  173,  174. 

sea,  305,  310,  314,  316,  318. 

Climate,  56,  59,  82,  102,  135. 

and  animals,  348,  354. 

and  land  forms,  278,  283. 

and  man,  84,  349. 

and  plants,  83,  348,  353. 

and  shore  lines,  323. 

changes  of,  288,  318,  338. 

dry,  135,  159,  180,  281,  359, 

362. 

glacial,  290. 

of  lands,  83,  133,  284. 

of  mountains,    71,   183,   188, 

189,  353. 

of  oceans,  52,  83,  84,  102. 

of  plains,  71,  188,  189. 

of  plateaus,  165. 

Cloudbursts,  66,  166,  234,  282. 
Clouds,  37,  39,  44,  62. 
Coal,  139,  170,  366. 
Coastal  plains,  143,  147,  158. 

ancient,  161. 

Atlantic,  148,  155,  158,   170. 

belted,  150. 

embayed,  154. 


Coasts,  107,  141,  211,  288,  304,  306, 

308,  316,  325,  368. 
Cold  wave,  78,  81. 
Colorado,  188,  226,  282,  294. 
Colorado  canyon  and  river,  165, 

166,  3^7. 
Columbia,  157,  158. 
Columbia  river,  198,  229. 
Commerce,   5,  97,  349,  364,  370. 
Compass,  18. 

Condensation  of  vapor,  16,  39,  62. 
Conduction,  28,  31,  61. 
Cones,  219,  220,  see  Volcanoes. 
Connecticut,  208,  368. 
Connecticut  river,  209. 
Conseguina,  223. 

Continental  divide,  198,  232,  243. 
Continental  shelf,  107,  133. 
Continents,  58,  129,  132,  341,  346. 
Contours,  222. 
Convection,  36,  60. 
Coral  reefs,  see  Reefs. 
Corn,  76,  343,  348. 
Corona,  64. 
Cotopaxi,  223. 
Cotton,  148,  149,  348. 
Crater,  218,  221. 
Cuba,  106,  318,  325,  328,  366. 
Cuesta,  153. 

Cumberland  plateau,  167. 
Cumulus,  63. 
Currents,  114,  116,  118,  119,  120, 

122,  306,  308. 
Cyclones,^  46,  63,  67,  76,  80,  81. 

Day  and  night,  7,  13,  28,  48. 
Dead  sea,  284,  286. 
Deception  island,  221. 
Deerfield  river,  209. 


392 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Degrees,  9,  10. 
Delaware,  368. 
Delaware  bay  and  river,  152,  155, 

269,  273,  368. 
Deltas,  138,  212,  267,  269,  321,  322. 

in  lakes,  250,  267,  289. 

Denudation,  137,  see  Erosion. 

Denver,  282. 

Deposition  of  waste,  108,  137,  265, 

267,  283,  287. 
Deserts,  3^,  41,  71,  133,  278,  280, 

286,  288,  359. 
Dew,  61,  62. 

Dikes,  132,  266,  308,  322. 
Distributaries,  268,  322. 
Distribution  of  life,  332. 
Divides,  190,  198,  242,  243. 
Doldrums,  43,  44,  56,  60,  65,  67,  68. 
Drainage,  168,  180,  234,  243,  248, 

270,  284. 
Drift,  glacial,  296,  300,  302. 

of  ocean,  116,  117. 

Drought,  76,  236,  244,  359. 
Drumlins,  299. 
Dunes,  136,  287,  308,  309. 
Dust,  286,  287. 
Dwarfs,  350. 

Earth,  1,  332. 

age,  17. 

area,  129. 

astronomic  relations,  11,  12, 

14,  46. 

attraction,  5,  17,  24. 

axis,  6,  354. 

crust,  16,  132,  137,  177. 

interior,  15,  16. 

proofs  of  shape,  2,  3,  19. 

revolution,  11,  46,  48,  49,  87.      Fiji  islands,  68,  99. 


Earth,  rotation,  6,  7,  19,  36,  57,  85. 

shape  and  size,  1,  3,  4,  6. 

structure,  15. 

Earthquakes,  175, 180, 182, 201, 217, 

218,  224. 
Earthquake  waves,  113,  114. 
Eclipse,  2. 
Ecuador,  223. 
Eddies,  115,  117. 
Egypt,  135,  363. 
Electricity,  19,  65,  253. 
Enchanted  mesa,  172. 
England,  139,  162,  242,  314. 
Equator,  9,  29,  36,  102. 

heat,  35,  40,  49,  67,  83. 

sky,  89. 

Equatorial  calms,  43,  55,  57. 

rains,  54,  56,  72,  74,  83. 

Equinox,  88. 

Erosion,  137,  185,  245,-308,  311. 

glacial,  294,  299,  320. 

Eruptions,  219,  223,  225,  228,  231. 

Escarpment,  173. 

Eskimos,  103,  292,  324,  352. 

Estuaries,  121. 

Eurasia,  5Q,  129,  345,  356. 

Europe,  55,  72,  81,  84,  104,  129, 

345,  346. 
Exercises,  4,  8,  10,  12,  35,  42,  45, 

50,  51,  53,  61,  75,  83,  85,  87,  90, 

115,  259,  260,  261,  264. 

Fall  line,  157,  158. 

Falls,  157,  247,  248,  251,  299,  302. 

Famines,  266. 

Fans,  179,  197,  265,  267,  268,  283. 

Faults,  174. 

Fertilizers,  150,  152,  330. 


INDEX 


393 


Fingal's  cave,  312. 

Fiords,  212,  320,  322. 

Fire,  24. 

Fish,  16,  100,  335,  336,  339, 

Fisheries,  109,  124,  156,  212,  320. 

Floe  ice,  102,  117. 

Flood  plains,  258,  261,  264,  268,  270, 

363. 
Floods,  194,  244,  250,  256, 264,  266, 

281,  282. 

and  lakes,  194,  250. 

sea,  69,  308. 

Foehn  wind,  18a. 

Fog,  64. 

Forests,  149,  159,  168,  170,  348. 

effects  of,  236,  310,  350. 

on  mountains,  41,  43, 187, 189, 

192,  204,  205,  355. 
Fort  Wayne,  320. 
Fossils,  108, 133, 161, 183, 185, 333, 

337. 
France,  310,  311,  313. 
Frigid  zone,  29,  75,  80. 
Frost,  61,  62,  135. 
Fundy,  Bay  of,  121. 

Galapagos,  119,  326,  348. 

Gales,  38,  80. 

Galung-gung,  223. 

Galveston,  69,  238. 

Ganges,  195,  268. 

Gases,  15,  23,  24,  100,  216,  218. 

Geology,  158. 

Geosphere,  17. 

Germany,  272,  295. 

Geysers,  239. 

Gibraltar,  106,  315. 

Glacial  period,  295,  319. 

Glacier,  104, 188,  279, 292,  294,  322. 


Glacier,  Alpine,  187,  260,  292,  296. 

ancient,  294,  299. 

continental,  290,  296. 

Laurentian,  295. 

Scandinavian,  296. 

valley,  292,  294. 

Glens,  205. 

Globigerina,  105. 

Gloucester,  109. 

Gold,  139,  191. 

Gorges,  184,  201,  251,  301. 

Grand'canyon,  165. 

Grand  Rapids,  302. 

Granite,  234. 

Gravity,  5,  24,  358. 

Grazing,  56,  71,  74,  160,  181,  294, 

354,  359. 
Great  Barrier  reef,  327. 
Great  Britain,  370. 
Great  lakes,  248,  284,  295,  319. 
Great  plains,  71,  73,  158,  366. 
Greek  philosophers,  3,  19. 
Greely,  103. 

Greenland,  104,  291,  321,  335,  361. 
Greenwich,  meridian  of,  10. 
Ground  water,  234,  236,  239,  283, 

362. 
Guam,  99. 

Guiana,  118,  158,  173. 
Gulf  Stream,  116,  118. 

Hail,  70. 
Halo,  63. 
Harbors,  40, 119, 120, 143, 147, 152, 

212,  307,  311,  320,  368. 
Harrisburg,  274. 
Hawaiian  islands,  106,  326. 
Headlands,  311,  314,  317. 
Heat,  24,  28,  30,  46. 


394 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Height  of  land,  241,  319. 

Hell  Gate,  122. 

Hemispheres,  9,  46,  52,  53,  54,  96. 

Herculaneum,  224. 

Highlands  of  Scotland,  205,  318. 

Himalayas,  71,  185,  189,  193,  200, 

202,  294. 
History  and  nature,  170,  205,  321, 

357,  361,  367. 
Hoang-Ho,  265,  268. 
Horizon,  19. 

Horse  latitudes,  44,  45,  55. 
Hot  springs,  239. 
Hudson  bay,  50. 
Hudson  river,  368. 
Humboldt  current,  118. 
Humidity,  60. 
Hungary,  262. 
Hurricane  ledge,  173,  175. 
Hurricanes,  67,  69,  112. 

Ibex,  356. 

Ice,  15,  63,  102,  117,  279,  291,  323. 

falls,  192. 

sheets,  290,  291,  294,  319. 

See  Glaciers. 
Icebergs,  104,  291,  292. 
Iceland,  226,  228,  239. 
Idaho,  229. 
Illinois,  320. 
India,  72,  189,  194,  269. 
Indiana,  320.  " 
Indian  ocean,  58,  68,  69,  96,  115, 

226. 
Indians,  172,  321,  361. 
Inlets,  152,  308. 
Instinct,  341. 
Intelligence,  341. 
Iowa,  238. 


Ireland,  116. 
Iron  ore,  139,  170,  366. 
Irrigation,  56,  71,  159,  265,  362. 
Islands,  50,  131,  314,  320,  346,  370. 

continental,  211,  212,  311. 

coral,  106,  325,  328,  330. 

oceanic,  106,  131. 

volcanic,   106,  219,  225,  226, 

348. 
Isobars,  91. 

Isothermal  lines,  33,  35,  48,  50,  53. 
Italy,*  225,  269,  314. 

Jaguar,  343. 

Japan,  114,  203,  225,  345. 

Java,  223. 

Jetties,  322. 

Jorullo,  219. 

Jura,  183,  184. 

Kanawha  river,  169. 
Kangaroo,  344. 
Katahdin,  Mt.,  357. 
Kentucky,  170,  235. 
Kittatinny  Mountain,  273. 
Krakatoa,  27,  113,  225. 

L<abrador,  51,  119,  370. 

Lagoons,  308,  328. 

Lake  Bonneville,  288,  319. 

Crater,  222. 

Erie,  248,  251,  320. 

Geneva,  250,  267. 

Great  Salt,  284,  288,  290. 

Lahontan,  289. 

Lob,  285. 

Michigan,  320. 

Nicaragua,  231. 

Nyassa,  249. 


INDEX 


896 


Lake  Ontario,  248,  261. 

Superior,  248,  366. 

Titicaca,  290. 

Van,  284. 

Victoria  Nyanza,  249. 

Lakes,  160,  230,  235,  247,  249,  263, 
284,  289,  319. 

African,  249. 

glacial,  296,  300. 

in  mountains,  197. 

salt,  181,  283. 

shore  lines,  133,  288,  318. 

temperature,  102. 

volcanic,  222,  228,  249. 

Land  and  sea  breezes,  59. 
Land  hemisphere,  96,  129,  341. 
Lands,  129. 

altitude,  4,  131,  132. 

area,  129. 

distribution,  130. 

features,  133,  141,  177,  266. 

life  on,  338. 

products,  138. 

surface,  20,  133,  134,  136. 

winds  on,  59. 

Land  sculptui-e,  186,  see  Waste. 
Landslides,  138,  193,  202. 
Language,  4,  205,  226,  357. 
Latitude,  8,  10,  54,  89,  342. 
Laurentian  highlands,  247,  295. 
Lava,  15,  16,  216,  225,  330. 

flows,  219,  227,  230,  249. 

plateaus,  227,  228,  229. 

Lawrence,  302. 

Ledges,  135,  247,  286,  306. 

Levees,  264. 

Life,  17,  24,  122,  332. 

Light,  24,  27,  64,  66,  124. 

Limestone,  139,  236. 


Llanos,  344,  363. 
London,  96. 
Long  Branch,  309. 
Long  Island  sound,  208. 
Longitude,  8. 
Lowell,  302. 
Luray  cavern,  236. 

Magellan,  3. 
Magnetic  poles,  18,  19. 
Magnetism,  terrestrial,  17,  332. 
Maine,  212,  297,  311,  367. 
Malay  peninsula,  58,  366. 
Mainmals,  340. 
Mammoth,  134. 
Mammoth  cave,  235. 
Man,  1,  189,  204,  345. 

and  nature,  332,  see  Nature. 

civilized,  364,  see  Civilization. 

in  deserts,  360. 

in  mountains,  204,  205,  357. 

savage,  329,  349,  365,  371. 

warfare,  369. 

Manchester,  302. 

Mangrove,  324. 

Manufactures,  139,  157,  169,  209, 

252,  301,  364,  370,  371. 
Maps,  386. 

Marshes,  152,  160,  170,  308. 
Marsupials,  344,  347. 
Maryland,  211,  238,  274,  368. 
Massachusetts,  132,  208,  299. 
Meander  belt,  263. 
Meanders,  261,  271,  273. 
Mediterranean,  106,  226. 
Merced  river,  265. 
Meridians,  8,  9,  10,  11. 
Merrimac,  302. 
Mesa,  171,  172. 


396 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Meteors,  23. 

Mexico,  41,  146,  226,  280. 

Gulf  of,  74,  107,  118,  322. 

Mining,  139,  170,  183,  333. 

Minneapolis,  302. 

Minnesota,  366. 

Mirage,  30,  286. 

Mississippi  river  and  valley,  65,  67, 

71,  74,  76,  138, 255,  262,  264,  319. 

delta,  268,  322. 

flood  plain,  264. 

meanders,  262,  263,  264. 

Missouri,  271,  278. 

river,  198. 

Mist,  64. 
Mohawk,  258. 
Monadnock,  207. 
Monsoons,  57,  58,  72. 
Monte  Nuovo,  218. 
Months,  47,  48,  50. 
Moon,  2,  13,  124. 
Moraines,  293,  295,  297. 
Mountains,  43,  133,  177. 

air  on,  26,  29. 

block,  178. 

buried,  285. 

climate  of,  188. 

dissected,  181,  196,  301. 

effects  of,  170,  180,  185,  189, 

356,  357,  369. 

embayed,  211. 

folded,  183,  210. 

growing,  201,  204. 

lofty,  27,  185,  188,  196,  204, 

355. 

old,  196,  206,  210. 

— -subdued,  204,  301. 

worn-down,  206. 

young,  180,  204,  205. 


Mt.  Blanc,  187,  295. 
Mt.  Mazama,  222,  230. 
Mud  volcanoes,  241. 

Nansen,  103,  117. 

Narragansett  bay,  368. 

Natural  bridge,  236. 

Nature  and  man,  170,  204, 205,  321, 

332,  357,  361,  364,  367. 
Navigation,  10, 18, 40,  43,  58, 69,  81 , 

97,  104,  116,  118,  120,  248,  370. 

river,  157,  365. 

Nebraska,  283. 
Nebular  hypothesis,  14. 
Neckar  river,  272. 
Netherlands,  132,  309,  310. 
Nevada,  73,  178,  181,  204,  280,  283. 
New  England,  80,   109,  209,  212, 

255,  298,  313. 
Newfoundland,  104,  109,  119. 
New  Hampshire,  207,  357. 
New  Jersey,  112, 132, 152,  308,  366, 

368. 
New  Mexico,  171,  172,  230. 
New  Orleans,  323. 
Newton,  6. 
New  York,  239,  258,  301,  366,  368. 

city,  122,  369. 

New  Zealand,  96,  131. 

Niagara,  138,  248,  251. 

Nile,  56,  249,  363. 

Nimbus,  64. 

Nitrogen,  24. 

Nomads,  160. 

Noon,  7,  8,  88. 

Norfolk,  156. 

Normandy,  311,  321. 

North  America,  43,  72,  78,  80,  107, 

344,  346. 


INDEX 


397 


North  Carolina,  74,  148,  160,  206,      Pacific  ocean,  68,  80,  84,  96, 


318. 
North  Dakota,  298.   . 
Northern  lights,  18. 
Northmen,  321. 
North  pole,  9,  18,  36. 
North  Star,  6. 
Norway,  119,  226,  299,  318,  320. 

Oases,  361. 


105,  115,  119,  226,  328. 
Pacific  slope,  43,  72. 
PamUco  sound,  155. 
Pampas,  190,  344,  366. 
Panama,  315,  316. 
Parallels,  9,  10. 
Parana,  56. 
Pass,  190. 
Patagonia,  190,  292,  3TS,  32; 


Occupations,  52, 157,  162, 169, 170,      Peaks,  178,  185,  186,  191,  366. 
185,  209,  258,  358,  364,  365,  366,       Pelee,  223. 
370,  371. 


Ocean,  96,  304. 

action,  107,  112,  121,  306. 

air,  60,  100. 

bottom,-  98,  105,  123. 

.color,  100. 

composition,  100. 

currents,  114,  116,  118. 

density,  100. 

depth,  96,  99,  132. 

distribution,  15,  96,  129,  130. 

explorations,  3,  98,  103. 

form,  96. 

life  in,  100,  105,  122,  338. 

phosphorescence,  100,  124. 

storms,  80. 

temperature,  28,  98,  101, 107. 

-»— waves,  109,  111,  113. 
Ohio,  168,  170. 


Peneplain,  206,  208,  210,  246. 

Pennsylvania,  210,  271,  273,  366. 

Perihelion,  12. 

Persia,  285. 

Peru,  60,  71,  359. 

Peruvian  current,  118,  326. 

Philadelphia,  158. 

Philippine  islands,  3,  69. 

Piedmont  belt,  149,  206,  243,  271. 

Pikes  peak,  356. 

Pittsburg,  170. 

Plains,  141,  158,  161,  369. 

coastal,  143, 147, 160, 154, 269, 

307,  318. 

glacial,  296. 

river-made,    266,     see    Flood 

plains. 
Planetary  circulation,  37,  40. 
Planetary  winds,  39. 


Ohio  river  and  valley,  71,  170,  250.       Planets,  12,  13,  14,  17,  19. 


Ooze,  105. 

Oregon,   146,   178,   182,  204,  229, 

249. 
Osage  river,  271. 
Ox-bow  lake,  263. 
Oxygen,  24. 
Ozark  plateau,  278. 


distance  and  diameter,  14. 

Plants,  24,  62,  83,  235,  341,  346, 
353. 

distribution,  332,  337,  348. 

in  oceans,  123,  124,  338. 

on  deserts,  359,  362. 

on  mountains,  366. 


398 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Plants  on  plateaus,  165. 
Plateaus,  162,  165,  171,  173. 

dissected,  167,  278. 

Platforms,  163,  318. 

Platte  river,  261. 

Po,  295. 

Polar  regions,  29,  64,  72,  75,  290. 

Poles,  9,  18,  29. 

Pompeii,  223. 

Population,  169,  170,  189,  370,  371. 

of  mountains,  201,  204,  357. 

of  river-made  plains,  258,  260, 

269,  270,  363. 
See  Settlements. 
Porto  Rico,  100. 

Ports,  147,  157,  309,  see  Harbors. 
Potomac  river,  211,  269,  368. 
Prairies,  71,  170,  296,  366. 
Prevailing     westerly     winds,     see 

Winds. 
Prime  meridian,  10. 
Problems,  9,  10,  35,  50,  90. 
Products,  138. 

Promontories,  211,  311,  313. 
Pyrenees,  190,  357. 

■Race,  tidal,  122. 

Races  of  men,  189,  204,  205,  345. 

Radiation,  28,  46,  61. 

Railroads,  97,  160,  191,  201,  371. 

Rainbow,  6Q. 

Rainfall,  38,  44,  65,  70,  72,  234. 

and  trade  winds,  41,  44,  55.    • 

and  westerly  winds,  43,  55, 

159. 
distribution  of,  41,  43,  56,  59, 

71,  72,  180,  183,  188,  280,  359. 

equatorial,  56,  72,  74,  83. 

subequatorial,  56,  353. 


Rainfall,  subtropical,  55,  56,  354. 

Rain  gauge,  70- 

Raleigh,  158.  • 

Rapids,  166,  247,  251,  255. 

Reaches,  255. 

Reefs,  coral,  324,  326,  327. 

sand,  152,  156,  808,  313,  314. 

Refraction,  64,  66. 

Reindeer,  342. 

Relief,  147,  185,  210,  284. 

Rhine,  309. 

Rhode  Island,  368. 

Rhone,  250. 

Richmond,  158. 

Ridges,  185,  186,  190. 

Rio  Grande,  323. 

Rivers,    241,   245,    261,    265,   269, 

302. 

graded,  254. 

mature,  246,  254,  269. 

old,  246,  270. 

revived,  271. 

withering,  281,  283,  285. 

young^  246^  257^  271. 

Roads,  143,    156,    169,    185,    190, 

209,  247,  256,  258,  318,  320. 
Rochester,  302. 
Rock  basins,  296,  300. 
Rock  waste,  see  Waste. 
Rocks,  15,  108,  134,  136,  138,  235. 
Rocky  mountains,  71,  74,  185,  188, 

200,  239,  243,  281,  294. 
Roraima,  173. 
Rotation  of  earth,  6,  7,  36,  57,  85. 

Sahara,  41,  42,  50,  56,  71,  83,  280, 

286,  354,  361,  362. 
Salinas,  290. 
Salt,  290,  see 


INDEX 


399 


Sand,  286,  308,  310. 

reefs,  sec  Reefs. 

Sandstone,  107,  209. 

San  Francisco,  369. 

Saratoga  Springs,  239. 

Sargassum,  123. 

Satellites,  13. 

Saturation,  60. 

Sault  Ste.  Marie,  248. 

Savannahs,  148.  . 

Scandinavia,  296,  321. 

Schuylkill,  153,  158. 

Scotland,  145,  205,  317,  318. 

Seas,  106. 

Seasons,  46,  49,  50,  56,  76,  77,  78, 

83,  353. 
Seaweed,  123. 

Sediment,  101,  106,  108,  121,  148. 
Seine,  121. 

Selkirk  mountains,  188. 
Settlements   on    coasts,    143,    156, 

212,  314,  318,  320,  368. 

deserts,  285,  361,  363. 

mountains,  181,  183,  185,  216. 

plains,  146,  159,  206,  297. 

plateaus,  165,  166,  171,  278. 

rivers,  209,  252,  258,  302,  363. 

See  Population. 
Shasta,  Mt.,  222,  229,  231. 
Sheavwits  plateau,  173,  174. 
Ships,  4,  40,  69,  98,  103,  120,  212. 
Shir^  river,  249. 
Shore  lines,  132,  155,  304,307,  311, 

317,  .323. 

of  deltas,  322. 

of  lakes,  133,  288,  318. 

Siberia,  81,  134,  160. 
Sierra  Nevada,  73,  189,  296. 
Silt,  255,  263,  265,  269. 


Sink  holes,  235. 

Sirocco,  81. 

Siwa,  363. 

Sky,  19,  27,  62,  76,  78,  89. 

Snake  river,  229,  288. 

Snow,  70,  77,  187,  190,  192,  290. 

line,  29,  355.  • 

Soil,  23,    135,  148,  162,  158,  296, 

362. 
Solar  system,  14,  17. 
Solstice,  88. 
Sound,  27,  66,  340. 
Sounding,  98. 
Sounds,  212. 

South  America,  343,  344,  346,  366. 
South  Carolina,  1.48,  157. 
Spain,  1.39. 

Springs,  236,  230,  361. 
St.  Bernard  pass,  190. 
St.  Gotthard,  193. 
St.  Helena,  112. 
St.  Lawrence,    80,    247,    248,  250, 

284,  319. 
Stacks,  312,  317. 
Stars,  12,  19. 
Steppes,  354. 

Storms,  64,  65,  Qd,  67,  79,  80. 
Streams,  235,  2.36,  241,  281. 
Subequatorial  belts,  56,  71, -83,  353. 
Subtropical  belts,  55,  56,  73. 
Sudan,  83. 
Sulu  sea,  107. 

Sun,  7,  11,  14,  46,  48,  87,  125. 
Sunrise  and  sunset,  7,  27,  89,  225. 
Surf,  40,  58,  111,  304,  313. 
Susquehanna,  269,  271,  274,  368. 
Svanetians,  357. 
Swamps,  150,  296,  813,  324. 
Sweden,  132. 


400 


ELEMENTARY  PHYSICAL  GEOGRAPHY 


Swell,  111. 

Switzerland,  189,  199,  see  Alps. 

Table  mountains,  171. 

Talus,  163,  1G6,  173,  180. 

Tarim  river,  285. 

Temperate  zone,  59,  75,  78,  80,  84. 

Temperature   of    atmosphere,    28, 

32,  3r,  37,  46,  49,  6>. 

and  currents,  .118. 

charts,  33. 

mean  annual,  33,  34,  50. 

of  earth,  16,  134. 

of  lakes,  102. 

— -of  oceans,  28,  98,  101,  118. 
Terraces,  200. 
Texas,  74,  323. 
Thermograph,  32. 
Thermometer,  31,  32. 
Thunderstorms,  44,  65. 
Tiber,  138. 
Tibet,  28,  226. 
Tides,  119,  122,  126,  268,  304. 

cause  of,  120,  124. 

Time,  7,  11,  46,  49. 

Tin,  366. 

Tonga  islands,  219. 

Tornadoes,  66. 

Torrents,  197,  253,  254,  280. 

Torrid  zone,  29,   48,  59,   60,    74, 

80. 
Trade  winds,  39,  40,  55,  57,  71. 
Transportation  of  waste,  137,  164, 

168,  188,  196,  246,  270. 
Tree  line,  355. 
Trenton,  158. 
Tributaries,  168,  254. 
Tunnels,  191,  193. 
Turkestan,  285. 


Turks,  346. 
Typhoons,  67,  69. 

IJinkaret  plateau,  173. 

United  States,  158,  170,  191,  338, 

371. 

boundaries,  11,  368. 

coasts,  148,  158,  368. 

development,  371. 

glacial    acti^    in,   295,   296, 

302. 

products,  76,  139,  348,  371. 

rainfall,  72. 

weather,  75,  76,  77,  82,  291. 

winds,  42,  63,  79,  81. 

See  Rivers,  Lakes,  Plains,  etc. 
Utah,  71,  73,  181,  280,  283,  319. 

Valleys,.  136,  209,  256,  259,  270. 

crosswise,  200. 

drowned,  154,  156,  269,  368. 

filled,  199.    ■ 

hanging,  299,  300,  322. 

in  mountains,  185,  196,  368. 

in  plains,  143,  145,  154,  159. 

in  plateaus,  162. 

lengthwise,  200. 

terraced,  200. 

Vapor,  38,  41,  60,  62. 

Variation  of  plants  and  animals, 

337,  338. 
Vegetation,  43,  159,  181,  187,  235, 

350,  353,  355,  359. 
Venezuela,  56,  353. 
Vera  Cruz,  147. 
Vermont,  208. 
Vesuvius,  221,  223. 
Vikings,  321. 
Vineyard  sound,  67. 


% 


INDEX 


401 


Virginia,  156,  206,  210,  318,  368. 
Volcanoes,  10,  100,  113,  133,  215, 
210,  220,  223,  226,  229,  231. 

Wadies,  281. 
_  Wales,  205. 

'Washington,  72,  229,  366. 
Waste  of  tlie  land,  134,  136,  163, 

245,  254. 

and  climate,  135,  323. 

deposition  of,   108,  137,  265, 

207,  283,  287. 

glacial,  279,  293,  296. 

in  basins,  284,  209. 

in  valleys,  183,  197,  199,  281. 

on  shores,  107,  112,  141,  304. 

transportation   of,    137,    104, 

108,  188,  190,  240,  270. 
Water,  15,  38,  90,  102,  130,  234. 

circulation  of,  39. 

hemisphere,  90,  129. 

power,"  252,  301,  302. 

Waterfalls,  see  Falls. 

Water  gaps,  210,  273. 

Watershed,  iee  Divide. 

Waterspouts,  6Q. 

Water  vapor,  see  Vapor,  Eainfall. 

Waves,  109,    111,   804,   300,   308, 

811,  316. 

earthquake,  113. 

Weather,  42,  59,  74,  76,  77,  78. 

bureau,  82,  90. 

maps,  33,  81,  90. 

prediction,  81. 

Weathering,    134,    163,    183,    186, 

200,  205,  206,  209,  312. 
Wells,  237,  238. 


West  Indies,  69,  106,  133,  325. 

West  Virginia,  167,  170,  236,  278. 

Wheat,  77,  348. 

Whirlwinds,  66,  286. 

White  mountains,  357. 

White  Sulphur  Springs,  2.39. 

Winds,  36,  37,  39,  79,  85,  91,  189. 

and  currents,  115. 

and  denudation,  136,  286. 

anticyclonic,  46,  75,  78,  80. 

cyclonic,  46,  63,  67,  75,  78, 

'  80,  81. 

daytime,  60. 

land  and  sea  breezes,  59. 

of  continents,  58. 

planetary,  37,  39. 

prevailing   westerly,    39,    42, 

44,  51,  54,  63,  72,  75,  80,  334. 

terrestrial,  53,  76,  77,  79. 

trade,  39,  40,  44,  55,  57,  71. 

velocity,  38. 

westerly,  see  prevailing  wes- 
terly. 

whirls,  39,  40,  42,  44. 

Windward  islands,  40. 

Wisconsin,  161,  238. 

World,  Old  and  New,  130,  343, 
367,  371. 

Yakima  river,  257. 
Yellow  sea,  101,  208. 
Yellowstone  park,  198,  239,  240. 
Yellowstone  river,  251. 
Yucca,  360. 

Zenith,  89. 

Zones,  29,  46,  48,  62,  34a 


Plate  A 
RELIEF  MAP  OF  THE  UNITED  STATES 

Plate  B 
THE   CHIEF   PHYSICAL   DIVISIONS   OF 
THE  UNITED  STATES 


PLATE  A. 


PJJLTE  B. 


Plate  C 
UNITED  STATES 


PLATE  C. 


Itude  92  West    from  87  Greenwich     82 


Jsr 


fululh 


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,    ^Sv  I  s  c  as 


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deuce 


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Galveston 


M.      E      X      I      C 


UNITED    STATES. 


SCALE    OF    MILES. 


50    100        200        300         -400         500        600. 


4e       T^Test   92     from       Greenwich  87 


^      TTEW  ENGLAND 

i^  ind  Cout  ot 

^  Hlddle  Atlutie  State*. 

(On  EnlargedSoOe.) 
SCALE  OF  MIUE8; 
0   25    pO       100        150       200 
Tlu  M.N.  Co. 


Plate  D 
NORTH  AMERICA 


Plate  E 
SOUTH  AMERICA 


PLATE    E. 


Plate  F 
EUROPE 


TTLATE  P. 


:iO         Longitude      West  20  from     Greenwich  10 


Plate  G 

ASIA 


PLATE  G. 


#    LongUula     Ea»t     from     Qregnwlcfi*^^^ 


-      -l 


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B 


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m    Greenwich  100 


Plate  H 
AFRICA 


PI.ATE  H. 


Plate  I 

AUSTRALASIA,  MALAY   ARCHIPELAGO 

AND  MICRONESIA 


PLATE  I. 


«f 


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